[GitHub] [nifi-minifi-cpp] szaszm commented on a change in pull request #784: MINIFICPP-1206 - Rework and test ExecutePythonProcessor, add in-place script support

[GitBox]

szaszm commented on a change in pull request #784:
URL: https://github.com/apache/nifi-minifi-cpp/pull/784#discussion_r425930634



##########
File path: libminifi/test/script-tests/PythonExecuteScriptTests.cpp
##########
@@ -29,6 +29,15 @@
 #include "processors/GetFile.h"
 #include "processors/PutFile.h"
 
+// ,-------------------------------------------------------------,
+// | ! |                      Disclaimer                     | ! |
+// |---'                                                     '---'
+// |                                                             |
+// | This file contains tests for the "ExecuteScript" processor, |
+// |         not for the "ExecutePython" processor.              |
+// |                                                             |
+// '-------------------------------------------------------------'

Review comment:
       I'm against ASCII art in the code.
   
   
https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#nl3-keep-comments-crisp

##########
File path: extensions/script/python/ExecutePythonProcessor.cpp
##########
@@ -46,144 +50,177 @@ core::Relationship 
ExecutePythonProcessor::Failure("failure", "Script failures")
 void ExecutePythonProcessor::initialize() {
   // initialization requires that we do a little leg work prior to onSchedule
   // so that we can provide manifest our processor identity
-  std::set<core::Property> properties;
-
-  std::string prop;
-  getProperty(ScriptFile.getName(), prop);
-
-  properties.insert(ScriptFile);
-  properties.insert(ModuleDirectory);
-  setSupportedProperties(properties);
-
-  std::set<core::Relationship> relationships;
-  relationships.insert(Success);
-  relationships.insert(Failure);
-  setSupportedRelationships(std::move(relationships));
-  setAcceptAllProperties();
-  if (!prop.empty()) {
-    setProperty(ScriptFile, prop);
-    std::shared_ptr<script::ScriptEngine> engine;
-    python_logger_ = 
logging::LoggerFactory<ExecutePythonProcessor>::getAliasedLogger(getName());
+  if (getProperties().empty()) {
+    setSupportedProperties({
+      ScriptFile,
+      ScriptBody,
+      ModuleDirectory
+    });
+    setAcceptAllProperties();
+    setSupportedRelationships({
+      Success,
+      Failure
+    });
+    valid_init_ = false;
+    return;
+  }
 
-    engine = createEngine<python::PythonScriptEngine>();
+  python_logger_ = 
logging::LoggerFactory<ExecutePythonProcessor>::getAliasedLogger(getName());
 
-    if (engine == nullptr) {
-      throw std::runtime_error("No script engine available");
-    }
+  getProperty(ModuleDirectory.getName(), module_directory_);
 
-    try {
-      engine->evalFile(prop);
-      auto me = shared_from_this();
-      triggerDescribe(engine, me);
-      triggerInitialize(engine, me);
+  valid_init_ = false;
+  appendPathForImportModules();
+  loadScript();
+  try {
+    if ("" != script_to_exec_) {
+      std::shared_ptr<python::PythonScriptEngine> engine = getScriptEngine();
+      engine->eval(script_to_exec_);
+      auto shared_this = shared_from_this();
+      engine->describe(shared_this);
+      engine->onInitialize(shared_this);
+      handleEngineNoLongerInUse(std::move(engine));
       valid_init_ = true;
-    } catch (std::exception &exception) {
-      logger_->log_error("Caught Exception %s", exception.what());
-      engine = nullptr;
-      std::rethrow_exception(std::current_exception());
-      valid_init_ = false;
-    } catch (...) {
-      logger_->log_error("Caught Exception");
-      engine = nullptr;
-      std::rethrow_exception(std::current_exception());
-      valid_init_ = false;
     }
-
+  }
+  catch (const std::exception& exception) {
+    logger_->log_error("Caught Exception: %s", exception.what());
+    std::rethrow_exception(std::current_exception());
+  }
+  catch (...) {
+    logger_->log_error("Caught Exception");
+    std::rethrow_exception(std::current_exception());
   }
 }
 
 void ExecutePythonProcessor::onSchedule(const 
std::shared_ptr<core::ProcessContext> &context, const 
std::shared_ptr<core::ProcessSessionFactory> &sessionFactory) {
   if (!valid_init_) {
-    throw std::runtime_error("Could not correctly in initialize " + getName());
-  }
-  context->getProperty(ScriptFile.getName(), script_file_);
-  context->getProperty(ModuleDirectory.getName(), module_directory_);
-  if (script_file_.empty() && script_engine_.empty()) {
-    logger_->log_error("Script File must be defined");
-    return;
+    throw std::runtime_error("Could not correctly initialize " + getName());
   }
-
   try {
-    std::shared_ptr<script::ScriptEngine> engine;
-
-    // Use an existing engine, if one is available
-    if (script_engine_q_.try_dequeue(engine)) {
-      logger_->log_debug("Using available %s script engine instance", 
script_engine_);
-    } else {
-      logger_->log_info("Creating new %s script instance", script_engine_);
-      logger_->log_info("Approximately %d %s script instances created for this 
processor", script_engine_q_.size_approx(), script_engine_);
-
-      engine = createEngine<python::PythonScriptEngine>();
-
-      if (engine == nullptr) {
-        throw std::runtime_error("No script engine available");
-      }
-
-      if (!script_file_.empty()) {
-        engine->evalFile(script_file_);
-      } else {
-        throw std::runtime_error("No Script File is available to execute");
-      }
+    // TODO(hunyadi): When using "Script File" property, we currently re-read 
the script file content every time the processor is on schedule. This should 
change to single-read when we release 1.0.0
+    // https://issues.apache.org/jira/browse/MINIFICPP-1223
+    reloadScriptIfUsingScriptFileProperty();
+    if (script_to_exec_.empty()) {
+      throw std::runtime_error("Neither Script Body nor Script File is 
available to execute");
     }
+    std::shared_ptr<python::PythonScriptEngine> engine = getScriptEngine();
 
-    triggerSchedule(engine, context);
+    engine->eval(script_to_exec_);
+    engine->onSchedule(context);
 
-    // Make engine available for use again
-    if (script_engine_q_.size_approx() < getMaxConcurrentTasks()) {
-      logger_->log_debug("Releasing %s script engine", script_engine_);
-      script_engine_q_.enqueue(engine);
-    } else {
-      logger_->log_info("Destroying script engine because it is no longer 
needed");
-    }
-  } catch (std::exception &exception) {
-    logger_->log_error("Caught Exception %s", exception.what());
-  } catch (...) {
+    handleEngineNoLongerInUse(std::move(engine));
+  }
+  catch (const std::exception& exception) {
+    logger_->log_error("Caught Exception: %s", exception.what());
+  }
+  catch (...) {
     logger_->log_error("Caught Exception");
   }
 }
 
 void ExecutePythonProcessor::onTrigger(const 
std::shared_ptr<core::ProcessContext> &context, const 
std::shared_ptr<core::ProcessSession> &session) {
+  if (!valid_init_) {
+    throw std::runtime_error("Could not correctly initialize " + getName());
+  }
   try {
-    std::shared_ptr<script::ScriptEngine> engine;
-
-    // Use an existing engine, if one is available
-    if (script_engine_q_.try_dequeue(engine)) {
-      logger_->log_debug("Using available %s script engine instance", 
script_engine_);
-    } else {
-      logger_->log_info("Creating new %s script instance", script_engine_);
-      logger_->log_info("Approximately %d %s script instances created for this 
processor", script_engine_q_.size_approx(), script_engine_);
-
-      engine = createEngine<python::PythonScriptEngine>();
-
-      if (engine == nullptr) {
-        throw std::runtime_error("No script engine available");
-      }
-
-      if (!script_file_.empty()) {
-        engine->evalFile(script_file_);
-      } else {
-        throw std::runtime_error("No Script File is available to execute");
-      }
+    // TODO(hunyadi): When using "Script File" property, we currently re-read 
the script file content every time the processor is on schedule. This should 
change to single-read when we release 1.0.0
+    // https://issues.apache.org/jira/browse/MINIFICPP-1223
+    reloadScriptIfUsingScriptFileProperty();
+    if (script_to_exec_.empty()) {
+      throw std::runtime_error("Neither Script Body nor Script File is 
available to execute");
     }
 
-    triggerEngineProcessor(engine, context, session);
-
-    // Make engine available for use again
-    if (script_engine_q_.size_approx() < getMaxConcurrentTasks()) {
-      logger_->log_debug("Releasing %s script engine", script_engine_);
-      script_engine_q_.enqueue(engine);
-    } else {
-      logger_->log_info("Destroying script engine because it is no longer 
needed");
-    }
-  } catch (std::exception &exception) {
-    logger_->log_error("Caught Exception %s", exception.what());
+    std::shared_ptr<python::PythonScriptEngine> engine = getScriptEngine();
+    engine->onTrigger(context, session);
+    handleEngineNoLongerInUse(std::move(engine));
+  }
+  catch (const std::exception &exception) {
+    logger_->log_error("Caught Exception: %s", exception.what());
     this->yield();
-  } catch (...) {
+  }
+  catch (...) {
     logger_->log_error("Caught Exception");
     this->yield();
   }
 }
 
+// TODO(hunyadi): This is potentially not what we want. See 
https://issues.apache.org/jira/browse/MINIFICPP-1222
+std::shared_ptr<python::PythonScriptEngine> 
ExecutePythonProcessor::getScriptEngine() {
+  std::shared_ptr<python::PythonScriptEngine> engine;
+  // Use an existing engine, if one is available
+  if (script_engine_q_.try_dequeue(engine)) {
+    logger_->log_debug("Using available [%p] script engine instance", 
engine.get());
+    return engine;
+  }
+  engine = createEngine<python::PythonScriptEngine>();
+  logger_->log_info("Created new [%p] script instance", engine.get());
+  logger_->log_info("Approximately %d script instances created for this 
processor", script_engine_q_.size_approx());

Review comment:
       This could be on a single log line.
   ```suggestion
     logger_->log_info("Created new [%p] script engine instance. Number of 
instances: approx. %d / %d.", engine.get(), script_engine_q_.size_approx(), 
getMaxConcurrentTasks());
   ```

##########
File path: libminifi/test/script-tests/ExecutePythonProcessorTests.cpp
##########
@@ -0,0 +1,276 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define CATCH_CONFIG_MAIN
+
+#include <memory>
+#include <string>
+#include <set>
+
+#include "../TestBase.h"
+
+#include "processors/GetFile.h"
+#include "python/ExecutePythonProcessor.h"
+#include "processors/LogAttribute.h"
+#include "processors/PutFile.h"
+#include "utils/file/FileUtils.h"
+
+namespace {
+
+#include <unistd.h>
+#define GetCurrentDir getcwd
+
+std::string GetCurrentWorkingDir(void) {
+  char buff[FILENAME_MAX];
+  GetCurrentDir(buff, FILENAME_MAX);
+  std::string current_working_dir(buff);
+  return current_working_dir;
+}
+
+class ExecutePythonProcessorTestBase {
+ public:
+    ExecutePythonProcessorTestBase() :
+      logTestController_(LogTestController::getInstance()),
+      
logger_(logging::LoggerFactory<org::apache::nifi::minifi::python::processors::ExecutePythonProcessor>::getLogger())
 {
+      reInitialize();
+    }
+    virtual ~ExecutePythonProcessorTestBase() {
+      logTestController_.reset();
+      logTestController_.setDebug<TestPlan>();
+      
logTestController_.setDebug<minifi::python::processors::ExecutePythonProcessor>();
+      logTestController_.setDebug<minifi::processors::PutFile>();
+      logTestController_.setDebug<minifi::processors::PutFile::ReadCallback>();
+    }
+
+ protected:
+    void reInitialize() {
+      testController_.reset(new TestController());
+      plan_ = testController_->createPlan();
+    }
+
+    std::string createTempDir() {
+      char dirtemplate[] = "/tmp/gt.XXXXXX";
+      std::string temp_dir = testController_->createTempDirectory(dirtemplate);
+      REQUIRE(!temp_dir.empty());
+      struct stat buffer;
+      REQUIRE(-1 != stat(temp_dir.c_str(), &buffer));
+      REQUIRE(S_ISDIR(buffer.st_mode));
+      return temp_dir;
+    }
+
+    std::string putFileToDir(const std::string& dir_path, const std::string& 
file_name, const std::string& content) {
+      std::string file_path(dir_path + utils::file::FileUtils::get_separator() 
+ file_name);
+      std::ofstream out_file(file_path);
+      if (out_file.is_open()) {
+        out_file << content;
+        out_file.close();
+      }
+      return file_path;
+    }
+
+    std::string createTempDirWithFile(const std::string& file_name, const 
std::string& content) {
+      std::string temp_dir = createTempDir();
+      putFileToDir(temp_dir, file_name, content);
+      return temp_dir;
+    }
+
+    std::string getFileContent(const std::string& file_name) {
+      std::ifstream file_handle(file_name);
+      REQUIRE(file_handle.is_open());
+      const std::string file_content{ 
(std::istreambuf_iterator<char>(file_handle)), 
(std::istreambuf_iterator<char>())};
+      file_handle.close();
+      return file_content;
+    }
+
+    std::string getScriptFullPath(const std::string& script_file_name) {
+      return SCRIPT_FILES_DIRECTORY + utils::file::FileUtils::get_separator() 
+ script_file_name;
+    }
+
+    const std::string TEST_FILE_NAME{ "test_file.txt" };
+    const std::string TEST_FILE_CONTENT{ "Test text\n" };
+    const std::string SCRIPT_FILES_DIRECTORY{ "test_scripts" };
+
+    std::unique_ptr<TestController> testController_;
+    std::shared_ptr<TestPlan> plan_;
+    LogTestController& logTestController_;
+    std::shared_ptr<logging::Logger> logger_;
+};
+
+class SimplePythonFlowFileTransferTest : public ExecutePythonProcessorTestBase 
{
+ public:
+  enum class Expectation {
+    OUTPUT_FILE_MATCHES_INPUT,
+    RUNTIME_RELATIONSHIP_EXCEPTION,
+    PROCESSOR_INITIALIZATION_EXCEPTION
+  };
+  SimplePythonFlowFileTransferTest() : ExecutePythonProcessorTestBase{} {}
+
+ protected:
+  void testSimpleFilePassthrough(const Expectation expectation, const 
core::Relationship& execute_python_out_conn, const std::string& 
used_as_script_file, const std::string& used_as_script_body) {
+    reInitialize();
+    const std::string input_dir = createTempDirWithFile(TEST_FILE_NAME, 
TEST_FILE_CONTENT);
+    const std::string output_dir = createTempDir();
+
+    addGetFileProcessorToPlan(input_dir);
+    if (Expectation::PROCESSOR_INITIALIZATION_EXCEPTION == expectation) {
+      REQUIRE_THROWS(addExecutePythonProcessorToPlan(used_as_script_file, 
used_as_script_body));
+      return;
+    }
+    REQUIRE_NOTHROW(addExecutePythonProcessorToPlan(used_as_script_file, 
used_as_script_body));
+    addPutFileProcessorToPlan(execute_python_out_conn, output_dir);
+
+    plan_->runNextProcessor();  // GetFile
+    if (Expectation::RUNTIME_RELATIONSHIP_EXCEPTION == expectation) {
+      REQUIRE_THROWS(plan_->runNextProcessor());  // ExecutePythonProcessor
+      return;
+    }
+    REQUIRE_NOTHROW(plan_->runNextProcessor());  // ExecutePythonProcessor
+    plan_->runNextProcessor();  // PutFile
+
+    const std::string output_file_path = output_dir + 
utils::file::FileUtils::get_separator() +  TEST_FILE_NAME;
+
+    if (Expectation::OUTPUT_FILE_MATCHES_INPUT == expectation) {
+      const std::string output_file_content{ getFileContent(output_file_path) 
};
+      REQUIRE(TEST_FILE_CONTENT == output_file_content);
+    }
+  }
+  void testsStatefulProcessor() {
+    reInitialize();
+    const std::string output_dir = createTempDir();
+
+    auto executePythonProcessor = 
plan_->addProcessor("ExecutePythonProcessor", "executePythonProcessor");
+    plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptFile.getName(),
 getScriptFullPath("stateful_processor.py"));
+    executePythonProcessor -> initialize();
+
+    addPutFileProcessorToPlan(core::Relationship("success", "description"), 
output_dir);
+    plan_->runNextProcessor();  // ExecutePythonProcessor
+    for (std::size_t i = 0; i < 10; ++i) {
+      plan_->runCurrentProcessor();  // ExecutePythonProcessor
+    }
+    plan_->runNextProcessor();  // PutFile
+    for (std::size_t i = 0; i < 10; ++i) {
+      plan_->runCurrentProcessor();  // PutFile
+      const std::string state_name = std::to_string(i);
+      const std::string output_file_path = output_dir + 
utils::file::FileUtils::get_separator() + state_name;
+      const std::string output_file_content{ getFileContent(output_file_path) 
};
+      REQUIRE(output_file_content == state_name);
+    }
+  }
+
+ private:
+  std::shared_ptr<core::Processor> addGetFileProcessorToPlan(const 
std::string& dir_path) {
+    std::shared_ptr<core::Processor> getfile = plan_->addProcessor("GetFile", 
"getfileCreate2");
+    plan_->setProperty(getfile, 
org::apache::nifi::minifi::processors::GetFile::Directory.getName(), dir_path);
+    plan_->setProperty(getfile, 
org::apache::nifi::minifi::processors::GetFile::KeepSourceFile.getName(), 
"true");
+    return getfile;
+  }
+
+  std::shared_ptr<core::Processor> addExecutePythonProcessorToPlan(const 
std::string& used_as_script_file, const std::string& used_as_script_body) {
+    auto executePythonProcessor = 
plan_->addProcessor("ExecutePythonProcessor", "executePythonProcessor", 
core::Relationship("success", "description"), true);
+    if ("" != used_as_script_file) {
+      plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptFile.getName(),
 getScriptFullPath(used_as_script_file));
+    }
+    if ("" != used_as_script_body) {
+        plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptBody.getName(),
 getFileContent(getScriptFullPath(used_as_script_body)));
+    }
+    executePythonProcessor -> initialize();
+    return executePythonProcessor;
+  }
+
+  std::shared_ptr<core::Processor> addPutFileProcessorToPlan(const 
core::Relationship& execute_python_outbound_connection, const std::string& 
dir_path) {
+    std::shared_ptr<core::Processor> putfile = plan_->addProcessor("PutFile", 
"putfile", execute_python_outbound_connection, true);
+    plan_->setProperty(putfile, 
org::apache::nifi::minifi::processors::PutFile::Directory.getName(), dir_path);
+    return putfile;
+  }
+};
+
+// Test for python processors for simple passthrough cases
+//
+// +-----------+     +--------------------------+       +-----------+
+// |  Getfile  |   .-+  ExecutePythonProcessor  |     .-+  PutFile  |
+// +-----------+  /  +  -  -  -  -  -  -  -  -  +    /  +-----------+
+// |  success  +-°   |    Attribute: Script     |   /   |  success  +-+ checked
+// +-----------+     +--------------------------+  /    +-----------+
+//                   |         success          +-°
+//                   +--------------------------+
+//                   |         failure          +-X either success or failure 
is hooked up
+//                   +--------------------------+
+//

Review comment:
       I'm against ASCII art in the code. GetFile -> ExecutePythonProcessor -> 
PutFile is enough detail in a comment IMO.
   
   
https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#nl3-keep-comments-crisp

##########
File path: libminifi/test/script-tests/ExecutePythonProcessorTests.cpp
##########
@@ -0,0 +1,276 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define CATCH_CONFIG_MAIN
+
+#include <memory>
+#include <string>
+#include <set>
+
+#include "../TestBase.h"
+
+#include "processors/GetFile.h"
+#include "python/ExecutePythonProcessor.h"
+#include "processors/LogAttribute.h"
+#include "processors/PutFile.h"
+#include "utils/file/FileUtils.h"
+
+namespace {
+
+#include <unistd.h>
+#define GetCurrentDir getcwd
+
+std::string GetCurrentWorkingDir(void) {
+  char buff[FILENAME_MAX];
+  GetCurrentDir(buff, FILENAME_MAX);
+  std::string current_working_dir(buff);
+  return current_working_dir;
+}
+
+class ExecutePythonProcessorTestBase {
+ public:
+    ExecutePythonProcessorTestBase() :
+      logTestController_(LogTestController::getInstance()),
+      
logger_(logging::LoggerFactory<org::apache::nifi::minifi::python::processors::ExecutePythonProcessor>::getLogger())
 {
+      reInitialize();
+    }
+    virtual ~ExecutePythonProcessorTestBase() {
+      logTestController_.reset();
+      logTestController_.setDebug<TestPlan>();
+      
logTestController_.setDebug<minifi::python::processors::ExecutePythonProcessor>();
+      logTestController_.setDebug<minifi::processors::PutFile>();
+      logTestController_.setDebug<minifi::processors::PutFile::ReadCallback>();
+    }
+
+ protected:
+    void reInitialize() {
+      testController_.reset(new TestController());
+      plan_ = testController_->createPlan();
+    }
+
+    std::string createTempDir() {
+      char dirtemplate[] = "/tmp/gt.XXXXXX";
+      std::string temp_dir = testController_->createTempDirectory(dirtemplate);
+      REQUIRE(!temp_dir.empty());
+      struct stat buffer;
+      REQUIRE(-1 != stat(temp_dir.c_str(), &buffer));
+      REQUIRE(S_ISDIR(buffer.st_mode));
+      return temp_dir;
+    }
+
+    std::string putFileToDir(const std::string& dir_path, const std::string& 
file_name, const std::string& content) {
+      std::string file_path(dir_path + utils::file::FileUtils::get_separator() 
+ file_name);
+      std::ofstream out_file(file_path);
+      if (out_file.is_open()) {
+        out_file << content;
+        out_file.close();
+      }
+      return file_path;
+    }
+
+    std::string createTempDirWithFile(const std::string& file_name, const 
std::string& content) {
+      std::string temp_dir = createTempDir();
+      putFileToDir(temp_dir, file_name, content);
+      return temp_dir;
+    }
+
+    std::string getFileContent(const std::string& file_name) {
+      std::ifstream file_handle(file_name);
+      REQUIRE(file_handle.is_open());
+      const std::string file_content{ 
(std::istreambuf_iterator<char>(file_handle)), 
(std::istreambuf_iterator<char>())};
+      file_handle.close();
+      return file_content;
+    }
+
+    std::string getScriptFullPath(const std::string& script_file_name) {
+      return SCRIPT_FILES_DIRECTORY + utils::file::FileUtils::get_separator() 
+ script_file_name;
+    }
+
+    const std::string TEST_FILE_NAME{ "test_file.txt" };
+    const std::string TEST_FILE_CONTENT{ "Test text\n" };
+    const std::string SCRIPT_FILES_DIRECTORY{ "test_scripts" };
+
+    std::unique_ptr<TestController> testController_;
+    std::shared_ptr<TestPlan> plan_;
+    LogTestController& logTestController_;
+    std::shared_ptr<logging::Logger> logger_;
+};
+
+class SimplePythonFlowFileTransferTest : public ExecutePythonProcessorTestBase 
{
+ public:
+  enum class Expectation {
+    OUTPUT_FILE_MATCHES_INPUT,
+    RUNTIME_RELATIONSHIP_EXCEPTION,
+    PROCESSOR_INITIALIZATION_EXCEPTION
+  };
+  SimplePythonFlowFileTransferTest() : ExecutePythonProcessorTestBase{} {}
+
+ protected:
+  void testSimpleFilePassthrough(const Expectation expectation, const 
core::Relationship& execute_python_out_conn, const std::string& 
used_as_script_file, const std::string& used_as_script_body) {
+    reInitialize();
+    const std::string input_dir = createTempDirWithFile(TEST_FILE_NAME, 
TEST_FILE_CONTENT);
+    const std::string output_dir = createTempDir();
+
+    addGetFileProcessorToPlan(input_dir);
+    if (Expectation::PROCESSOR_INITIALIZATION_EXCEPTION == expectation) {
+      REQUIRE_THROWS(addExecutePythonProcessorToPlan(used_as_script_file, 
used_as_script_body));
+      return;
+    }
+    REQUIRE_NOTHROW(addExecutePythonProcessorToPlan(used_as_script_file, 
used_as_script_body));
+    addPutFileProcessorToPlan(execute_python_out_conn, output_dir);
+
+    plan_->runNextProcessor();  // GetFile
+    if (Expectation::RUNTIME_RELATIONSHIP_EXCEPTION == expectation) {
+      REQUIRE_THROWS(plan_->runNextProcessor());  // ExecutePythonProcessor
+      return;
+    }
+    REQUIRE_NOTHROW(plan_->runNextProcessor());  // ExecutePythonProcessor
+    plan_->runNextProcessor();  // PutFile
+
+    const std::string output_file_path = output_dir + 
utils::file::FileUtils::get_separator() +  TEST_FILE_NAME;
+
+    if (Expectation::OUTPUT_FILE_MATCHES_INPUT == expectation) {
+      const std::string output_file_content{ getFileContent(output_file_path) 
};
+      REQUIRE(TEST_FILE_CONTENT == output_file_content);
+    }
+  }
+  void testsStatefulProcessor() {
+    reInitialize();
+    const std::string output_dir = createTempDir();
+
+    auto executePythonProcessor = 
plan_->addProcessor("ExecutePythonProcessor", "executePythonProcessor");
+    plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptFile.getName(),
 getScriptFullPath("stateful_processor.py"));
+    executePythonProcessor -> initialize();
+
+    addPutFileProcessorToPlan(core::Relationship("success", "description"), 
output_dir);
+    plan_->runNextProcessor();  // ExecutePythonProcessor
+    for (std::size_t i = 0; i < 10; ++i) {
+      plan_->runCurrentProcessor();  // ExecutePythonProcessor
+    }
+    plan_->runNextProcessor();  // PutFile
+    for (std::size_t i = 0; i < 10; ++i) {
+      plan_->runCurrentProcessor();  // PutFile
+      const std::string state_name = std::to_string(i);
+      const std::string output_file_path = output_dir + 
utils::file::FileUtils::get_separator() + state_name;
+      const std::string output_file_content{ getFileContent(output_file_path) 
};
+      REQUIRE(output_file_content == state_name);
+    }
+  }
+
+ private:
+  std::shared_ptr<core::Processor> addGetFileProcessorToPlan(const 
std::string& dir_path) {
+    std::shared_ptr<core::Processor> getfile = plan_->addProcessor("GetFile", 
"getfileCreate2");
+    plan_->setProperty(getfile, 
org::apache::nifi::minifi::processors::GetFile::Directory.getName(), dir_path);
+    plan_->setProperty(getfile, 
org::apache::nifi::minifi::processors::GetFile::KeepSourceFile.getName(), 
"true");
+    return getfile;
+  }
+
+  std::shared_ptr<core::Processor> addExecutePythonProcessorToPlan(const 
std::string& used_as_script_file, const std::string& used_as_script_body) {
+    auto executePythonProcessor = 
plan_->addProcessor("ExecutePythonProcessor", "executePythonProcessor", 
core::Relationship("success", "description"), true);
+    if ("" != used_as_script_file) {
+      plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptFile.getName(),
 getScriptFullPath(used_as_script_file));
+    }
+    if ("" != used_as_script_body) {
+        plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptBody.getName(),
 getFileContent(getScriptFullPath(used_as_script_body)));
+    }
+    executePythonProcessor -> initialize();
+    return executePythonProcessor;
+  }
+
+  std::shared_ptr<core::Processor> addPutFileProcessorToPlan(const 
core::Relationship& execute_python_outbound_connection, const std::string& 
dir_path) {
+    std::shared_ptr<core::Processor> putfile = plan_->addProcessor("PutFile", 
"putfile", execute_python_outbound_connection, true);
+    plan_->setProperty(putfile, 
org::apache::nifi::minifi::processors::PutFile::Directory.getName(), dir_path);
+    return putfile;
+  }
+};
+
+// Test for python processors for simple passthrough cases
+//
+// +-----------+     +--------------------------+       +-----------+
+// |  Getfile  |   .-+  ExecutePythonProcessor  |     .-+  PutFile  |
+// +-----------+  /  +  -  -  -  -  -  -  -  -  +    /  +-----------+
+// |  success  +-°   |    Attribute: Script     |   /   |  success  +-+ checked
+// +-----------+     +--------------------------+  /    +-----------+
+//                   |         success          +-°
+//                   +--------------------------+
+//                   |         failure          +-X either success or failure 
is hooked up
+//                   +--------------------------+
+//
+// testSimpleFilePassthrough(OUTPUT_FILE_MATCHES_INPUT, SUCCESS, "", 
"passthrough_processor_transfering_to_success.py");
+//
+// translates to
+//
+// GIVEN an ExecutePythonProcessor set up with a "Script Body" attribute that 
transfers to REL_SUCCESS, but not "Script File"
+// WHEN the processor is triggered
+// THEN any consumer using the success relationship as source should receive 
the transfered data
+//
+TEST_CASE_METHOD(SimplePythonFlowFileTransferTest, "Simple file passthrough", 
"[executePythonProcessorSimple]") {
+  // Expectations
+  const auto OUTPUT_FILE_MATCHES_INPUT          = 
SimplePythonFlowFileTransferTest::Expectation::OUTPUT_FILE_MATCHES_INPUT;
+  const auto RUNTIME_RELATIONSHIP_EXCEPTION    = 
SimplePythonFlowFileTransferTest::Expectation::RUNTIME_RELATIONSHIP_EXCEPTION;
+  const auto PROCESSOR_INITIALIZATION_EXCEPTION = 
SimplePythonFlowFileTransferTest::Expectation::PROCESSOR_INITIALIZATION_EXCEPTION;
+  // ExecutePython outbound relationships
+  const core::Relationship SUCCESS {"success", "description"};
+  const core::Relationship FAILURE{"failure", "description"};
+
+  // For the tests "" is threated as none-provided since no optional 
implementation was ported to the project yet
+
+  ////////////////////////////////////////////////////////////
+  // 0. Neither valid script file nor script body provided  //
+  ////////////////////////////////////////////////////////////
+
+  //                                          TEST EXPECTATION  OUT_REL        
USE_AS_SCRIPT_FILE  USE_AS_SCRIPT_BODY
+  testSimpleFilePassthrough(PROCESSOR_INITIALIZATION_EXCEPTION, SUCCESS,       
                "", "");  // NOLINT
+  testSimpleFilePassthrough(PROCESSOR_INITIALIZATION_EXCEPTION, FAILURE,       
                "", "");  // NOLINT
+  testSimpleFilePassthrough(PROCESSOR_INITIALIZATION_EXCEPTION, SUCCESS, 
"non_existent_script.py", "");  // NOLINT
+  testSimpleFilePassthrough(PROCESSOR_INITIALIZATION_EXCEPTION, FAILURE, 
"non_existent_script.py", "");  // NOLINT
+
+  ///////////////////////////////////////
+  // 1. Using script file as attribute //
+  ///////////////////////////////////////
+
+  //                                      TEST EXPECTATION  OUT_REL            
                     USE_AS_SCRIPT_FILE  USE_AS_SCRIPT_BODY
+  testSimpleFilePassthrough(     OUTPUT_FILE_MATCHES_INPUT, SUCCESS, 
"passthrough_processor_transfering_to_success.py", "");  // NOLINT
+  testSimpleFilePassthrough(RUNTIME_RELATIONSHIP_EXCEPTION, FAILURE, 
"passthrough_processor_transfering_to_success.py", "");  // NOLINT
+  testSimpleFilePassthrough(RUNTIME_RELATIONSHIP_EXCEPTION, SUCCESS, 
"passthrough_processor_transfering_to_failure.py", "");  // NOLINT
+  testSimpleFilePassthrough(     OUTPUT_FILE_MATCHES_INPUT, FAILURE, 
"passthrough_processor_transfering_to_failure.py", "");  // NOLINT
+  testSimpleFilePassthrough(RUNTIME_RELATIONSHIP_EXCEPTION, FAILURE,           
        "non_transferring_processor.py", "");  // NOLINT
+
+  ///////////////////////////////////////
+  // 2. Using script body as attribute //
+  ///////////////////////////////////////
+
+  //                                      TEST EXPECTATION  OUT_REL  
SCRIPT_FILE                        USE_AS_SCRIPT_BODY
+  testSimpleFilePassthrough(     OUTPUT_FILE_MATCHES_INPUT, SUCCESS, "", 
"passthrough_processor_transfering_to_success.py");  // NOLINT 
+  testSimpleFilePassthrough(RUNTIME_RELATIONSHIP_EXCEPTION, FAILURE, "", 
"passthrough_processor_transfering_to_success.py");  // NOLINT 
+  testSimpleFilePassthrough(RUNTIME_RELATIONSHIP_EXCEPTION, SUCCESS, "", 
"passthrough_processor_transfering_to_failure.py");  // NOLINT 
+  testSimpleFilePassthrough(     OUTPUT_FILE_MATCHES_INPUT, FAILURE, "", 
"passthrough_processor_transfering_to_failure.py");  // NOLINT 
+  testSimpleFilePassthrough(RUNTIME_RELATIONSHIP_EXCEPTION, FAILURE, "",       
            "non_transferring_processor.py");  // NOLINT
+
+  ////////////////////////////////
+  // 3. Setting both attributes //
+  ////////////////////////////////
+

Review comment:
       The all-/ and empty lines are redundant IMO.
   
   
https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#nl3-keep-comments-crisp

##########
File path: extensions/script/python/ExecutePythonProcessor.cpp
##########
@@ -46,144 +50,177 @@ core::Relationship 
ExecutePythonProcessor::Failure("failure", "Script failures")
 void ExecutePythonProcessor::initialize() {
   // initialization requires that we do a little leg work prior to onSchedule
   // so that we can provide manifest our processor identity
-  std::set<core::Property> properties;
-
-  std::string prop;
-  getProperty(ScriptFile.getName(), prop);
-
-  properties.insert(ScriptFile);
-  properties.insert(ModuleDirectory);
-  setSupportedProperties(properties);
-
-  std::set<core::Relationship> relationships;
-  relationships.insert(Success);
-  relationships.insert(Failure);
-  setSupportedRelationships(std::move(relationships));
-  setAcceptAllProperties();
-  if (!prop.empty()) {
-    setProperty(ScriptFile, prop);
-    std::shared_ptr<script::ScriptEngine> engine;
-    python_logger_ = 
logging::LoggerFactory<ExecutePythonProcessor>::getAliasedLogger(getName());
+  if (getProperties().empty()) {
+    setSupportedProperties({
+      ScriptFile,
+      ScriptBody,
+      ModuleDirectory
+    });
+    setAcceptAllProperties();
+    setSupportedRelationships({
+      Success,
+      Failure
+    });
+    valid_init_ = false;
+    return;
+  }
 
-    engine = createEngine<python::PythonScriptEngine>();
+  python_logger_ = 
logging::LoggerFactory<ExecutePythonProcessor>::getAliasedLogger(getName());
 
-    if (engine == nullptr) {
-      throw std::runtime_error("No script engine available");
-    }
+  getProperty(ModuleDirectory.getName(), module_directory_);
 
-    try {
-      engine->evalFile(prop);
-      auto me = shared_from_this();
-      triggerDescribe(engine, me);
-      triggerInitialize(engine, me);
+  valid_init_ = false;
+  appendPathForImportModules();
+  loadScript();
+  try {
+    if ("" != script_to_exec_) {
+      std::shared_ptr<python::PythonScriptEngine> engine = getScriptEngine();
+      engine->eval(script_to_exec_);
+      auto shared_this = shared_from_this();
+      engine->describe(shared_this);
+      engine->onInitialize(shared_this);
+      handleEngineNoLongerInUse(std::move(engine));
       valid_init_ = true;
-    } catch (std::exception &exception) {
-      logger_->log_error("Caught Exception %s", exception.what());
-      engine = nullptr;
-      std::rethrow_exception(std::current_exception());
-      valid_init_ = false;
-    } catch (...) {
-      logger_->log_error("Caught Exception");
-      engine = nullptr;
-      std::rethrow_exception(std::current_exception());
-      valid_init_ = false;
     }
-
+  }
+  catch (const std::exception& exception) {
+    logger_->log_error("Caught Exception: %s", exception.what());
+    std::rethrow_exception(std::current_exception());
+  }
+  catch (...) {
+    logger_->log_error("Caught Exception");
+    std::rethrow_exception(std::current_exception());
   }
 }
 
 void ExecutePythonProcessor::onSchedule(const 
std::shared_ptr<core::ProcessContext> &context, const 
std::shared_ptr<core::ProcessSessionFactory> &sessionFactory) {
   if (!valid_init_) {
-    throw std::runtime_error("Could not correctly in initialize " + getName());
-  }
-  context->getProperty(ScriptFile.getName(), script_file_);
-  context->getProperty(ModuleDirectory.getName(), module_directory_);
-  if (script_file_.empty() && script_engine_.empty()) {
-    logger_->log_error("Script File must be defined");
-    return;
+    throw std::runtime_error("Could not correctly initialize " + getName());
   }
-
   try {
-    std::shared_ptr<script::ScriptEngine> engine;
-
-    // Use an existing engine, if one is available
-    if (script_engine_q_.try_dequeue(engine)) {
-      logger_->log_debug("Using available %s script engine instance", 
script_engine_);
-    } else {
-      logger_->log_info("Creating new %s script instance", script_engine_);
-      logger_->log_info("Approximately %d %s script instances created for this 
processor", script_engine_q_.size_approx(), script_engine_);
-
-      engine = createEngine<python::PythonScriptEngine>();
-
-      if (engine == nullptr) {
-        throw std::runtime_error("No script engine available");
-      }
-
-      if (!script_file_.empty()) {
-        engine->evalFile(script_file_);
-      } else {
-        throw std::runtime_error("No Script File is available to execute");
-      }
+    // TODO(hunyadi): When using "Script File" property, we currently re-read 
the script file content every time the processor is on schedule. This should 
change to single-read when we release 1.0.0
+    // https://issues.apache.org/jira/browse/MINIFICPP-1223
+    reloadScriptIfUsingScriptFileProperty();

Review comment:
       Reload in onSchedule should stay even in the future IMO, as users should 
have a way to apply their script changes. For this reason, I recommend removing 
the TODO and issue comments from here. The issue refers to avoiding reload in 
onTrigger in the future, which would improve performance.
   
   idea, 100% optional:
   As an optimization we may want to check the last modified timestamp of the 
inode before reading the file.

##########
File path: extensions/script/python/ExecutePythonProcessor.cpp
##########
@@ -46,144 +50,177 @@ core::Relationship 
ExecutePythonProcessor::Failure("failure", "Script failures")
 void ExecutePythonProcessor::initialize() {
   // initialization requires that we do a little leg work prior to onSchedule
   // so that we can provide manifest our processor identity
-  std::set<core::Property> properties;
-
-  std::string prop;
-  getProperty(ScriptFile.getName(), prop);
-
-  properties.insert(ScriptFile);
-  properties.insert(ModuleDirectory);
-  setSupportedProperties(properties);
-
-  std::set<core::Relationship> relationships;
-  relationships.insert(Success);
-  relationships.insert(Failure);
-  setSupportedRelationships(std::move(relationships));
-  setAcceptAllProperties();
-  if (!prop.empty()) {
-    setProperty(ScriptFile, prop);
-    std::shared_ptr<script::ScriptEngine> engine;
-    python_logger_ = 
logging::LoggerFactory<ExecutePythonProcessor>::getAliasedLogger(getName());
+  if (getProperties().empty()) {
+    setSupportedProperties({
+      ScriptFile,
+      ScriptBody,
+      ModuleDirectory
+    });
+    setAcceptAllProperties();
+    setSupportedRelationships({
+      Success,
+      Failure
+    });
+    valid_init_ = false;
+    return;
+  }
 
-    engine = createEngine<python::PythonScriptEngine>();
+  python_logger_ = 
logging::LoggerFactory<ExecutePythonProcessor>::getAliasedLogger(getName());
 
-    if (engine == nullptr) {
-      throw std::runtime_error("No script engine available");
-    }
+  getProperty(ModuleDirectory.getName(), module_directory_);
 
-    try {
-      engine->evalFile(prop);
-      auto me = shared_from_this();
-      triggerDescribe(engine, me);
-      triggerInitialize(engine, me);
+  valid_init_ = false;
+  appendPathForImportModules();
+  loadScript();
+  try {
+    if ("" != script_to_exec_) {
+      std::shared_ptr<python::PythonScriptEngine> engine = getScriptEngine();
+      engine->eval(script_to_exec_);
+      auto shared_this = shared_from_this();
+      engine->describe(shared_this);
+      engine->onInitialize(shared_this);
+      handleEngineNoLongerInUse(std::move(engine));
       valid_init_ = true;
-    } catch (std::exception &exception) {
-      logger_->log_error("Caught Exception %s", exception.what());
-      engine = nullptr;
-      std::rethrow_exception(std::current_exception());
-      valid_init_ = false;
-    } catch (...) {
-      logger_->log_error("Caught Exception");
-      engine = nullptr;
-      std::rethrow_exception(std::current_exception());
-      valid_init_ = false;
     }
-
+  }
+  catch (const std::exception& exception) {
+    logger_->log_error("Caught Exception: %s", exception.what());
+    std::rethrow_exception(std::current_exception());
+  }
+  catch (...) {
+    logger_->log_error("Caught Exception");
+    std::rethrow_exception(std::current_exception());
   }
 }
 
 void ExecutePythonProcessor::onSchedule(const 
std::shared_ptr<core::ProcessContext> &context, const 
std::shared_ptr<core::ProcessSessionFactory> &sessionFactory) {
   if (!valid_init_) {
-    throw std::runtime_error("Could not correctly in initialize " + getName());
-  }
-  context->getProperty(ScriptFile.getName(), script_file_);
-  context->getProperty(ModuleDirectory.getName(), module_directory_);
-  if (script_file_.empty() && script_engine_.empty()) {
-    logger_->log_error("Script File must be defined");
-    return;
+    throw std::runtime_error("Could not correctly initialize " + getName());
   }
-
   try {
-    std::shared_ptr<script::ScriptEngine> engine;
-
-    // Use an existing engine, if one is available
-    if (script_engine_q_.try_dequeue(engine)) {
-      logger_->log_debug("Using available %s script engine instance", 
script_engine_);
-    } else {
-      logger_->log_info("Creating new %s script instance", script_engine_);
-      logger_->log_info("Approximately %d %s script instances created for this 
processor", script_engine_q_.size_approx(), script_engine_);
-
-      engine = createEngine<python::PythonScriptEngine>();
-
-      if (engine == nullptr) {
-        throw std::runtime_error("No script engine available");
-      }
-
-      if (!script_file_.empty()) {
-        engine->evalFile(script_file_);
-      } else {
-        throw std::runtime_error("No Script File is available to execute");
-      }
+    // TODO(hunyadi): When using "Script File" property, we currently re-read 
the script file content every time the processor is on schedule. This should 
change to single-read when we release 1.0.0
+    // https://issues.apache.org/jira/browse/MINIFICPP-1223
+    reloadScriptIfUsingScriptFileProperty();
+    if (script_to_exec_.empty()) {
+      throw std::runtime_error("Neither Script Body nor Script File is 
available to execute");
     }
+    std::shared_ptr<python::PythonScriptEngine> engine = getScriptEngine();
 
-    triggerSchedule(engine, context);
+    engine->eval(script_to_exec_);
+    engine->onSchedule(context);
 
-    // Make engine available for use again
-    if (script_engine_q_.size_approx() < getMaxConcurrentTasks()) {
-      logger_->log_debug("Releasing %s script engine", script_engine_);
-      script_engine_q_.enqueue(engine);
-    } else {
-      logger_->log_info("Destroying script engine because it is no longer 
needed");
-    }
-  } catch (std::exception &exception) {
-    logger_->log_error("Caught Exception %s", exception.what());
-  } catch (...) {
+    handleEngineNoLongerInUse(std::move(engine));
+  }
+  catch (const std::exception& exception) {
+    logger_->log_error("Caught Exception: %s", exception.what());
+  }
+  catch (...) {
     logger_->log_error("Caught Exception");
   }
 }
 
 void ExecutePythonProcessor::onTrigger(const 
std::shared_ptr<core::ProcessContext> &context, const 
std::shared_ptr<core::ProcessSession> &session) {
+  if (!valid_init_) {
+    throw std::runtime_error("Could not correctly initialize " + getName());
+  }
   try {
-    std::shared_ptr<script::ScriptEngine> engine;
-
-    // Use an existing engine, if one is available
-    if (script_engine_q_.try_dequeue(engine)) {
-      logger_->log_debug("Using available %s script engine instance", 
script_engine_);
-    } else {
-      logger_->log_info("Creating new %s script instance", script_engine_);
-      logger_->log_info("Approximately %d %s script instances created for this 
processor", script_engine_q_.size_approx(), script_engine_);
-
-      engine = createEngine<python::PythonScriptEngine>();
-
-      if (engine == nullptr) {
-        throw std::runtime_error("No script engine available");
-      }
-
-      if (!script_file_.empty()) {
-        engine->evalFile(script_file_);
-      } else {
-        throw std::runtime_error("No Script File is available to execute");
-      }
+    // TODO(hunyadi): When using "Script File" property, we currently re-read 
the script file content every time the processor is on schedule. This should 
change to single-read when we release 1.0.0
+    // https://issues.apache.org/jira/browse/MINIFICPP-1223
+    reloadScriptIfUsingScriptFileProperty();
+    if (script_to_exec_.empty()) {
+      throw std::runtime_error("Neither Script Body nor Script File is 
available to execute");
     }
 
-    triggerEngineProcessor(engine, context, session);
-
-    // Make engine available for use again
-    if (script_engine_q_.size_approx() < getMaxConcurrentTasks()) {
-      logger_->log_debug("Releasing %s script engine", script_engine_);
-      script_engine_q_.enqueue(engine);
-    } else {
-      logger_->log_info("Destroying script engine because it is no longer 
needed");
-    }
-  } catch (std::exception &exception) {
-    logger_->log_error("Caught Exception %s", exception.what());
+    std::shared_ptr<python::PythonScriptEngine> engine = getScriptEngine();
+    engine->onTrigger(context, session);
+    handleEngineNoLongerInUse(std::move(engine));
+  }
+  catch (const std::exception &exception) {
+    logger_->log_error("Caught Exception: %s", exception.what());
     this->yield();
-  } catch (...) {
+  }
+  catch (...) {
     logger_->log_error("Caught Exception");
     this->yield();
   }
 }
 
+// TODO(hunyadi): This is potentially not what we want. See 
https://issues.apache.org/jira/browse/MINIFICPP-1222
+std::shared_ptr<python::PythonScriptEngine> 
ExecutePythonProcessor::getScriptEngine() {
+  std::shared_ptr<python::PythonScriptEngine> engine;
+  // Use an existing engine, if one is available
+  if (script_engine_q_.try_dequeue(engine)) {
+    logger_->log_debug("Using available [%p] script engine instance", 
engine.get());
+    return engine;
+  }
+  engine = createEngine<python::PythonScriptEngine>();
+  logger_->log_info("Created new [%p] script instance", engine.get());
+  logger_->log_info("Approximately %d script instances created for this 
processor", script_engine_q_.size_approx());
+  if (engine == nullptr) {
+    throw std::runtime_error("No script engine available");
+  }
+  return engine;
+}
+
+void 
ExecutePythonProcessor::handleEngineNoLongerInUse(std::shared_ptr<python::PythonScriptEngine>&&
 engine) {
+  // Make engine available for use again
+  if (script_engine_q_.size_approx() < getMaxConcurrentTasks()) {
+    logger_->log_debug("Releasing [%p] script engine", engine.get());
+    script_engine_q_.enqueue(engine);
+  } else {
+    logger_->log_info("Destroying script engine because it is no longer 
needed");
+  }
+}
+
+void ExecutePythonProcessor::appendPathForImportModules() {
+  // TODO(hunyadi): I have spent some time trying to figure out pybind11, but
+  // could not get this working yet. It is up to be implemented later
+  // https://issues.apache.org/jira/browse/MINIFICPP-1224
+  if ("" != module_directory_) {
+    logger_ -> log_error("Not supported property: Module Directory.");

Review comment:
       I think spaces around the `->` operator look really strange and they are 
inconsistent with the file (or the codebase).

##########
File path: libminifi/test/script-tests/ExecutePythonProcessorTests.cpp
##########
@@ -0,0 +1,276 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define CATCH_CONFIG_MAIN
+
+#include <memory>
+#include <string>
+#include <set>
+
+#include "../TestBase.h"
+
+#include "processors/GetFile.h"
+#include "python/ExecutePythonProcessor.h"
+#include "processors/LogAttribute.h"
+#include "processors/PutFile.h"
+#include "utils/file/FileUtils.h"
+
+namespace {
+
+#include <unistd.h>
+#define GetCurrentDir getcwd
+
+std::string GetCurrentWorkingDir(void) {
+  char buff[FILENAME_MAX];
+  GetCurrentDir(buff, FILENAME_MAX);
+  std::string current_working_dir(buff);
+  return current_working_dir;
+}
+
+class ExecutePythonProcessorTestBase {
+ public:
+    ExecutePythonProcessorTestBase() :
+      logTestController_(LogTestController::getInstance()),
+      
logger_(logging::LoggerFactory<org::apache::nifi::minifi::python::processors::ExecutePythonProcessor>::getLogger())
 {
+      reInitialize();
+    }
+    virtual ~ExecutePythonProcessorTestBase() {
+      logTestController_.reset();
+      logTestController_.setDebug<TestPlan>();
+      
logTestController_.setDebug<minifi::python::processors::ExecutePythonProcessor>();
+      logTestController_.setDebug<minifi::processors::PutFile>();
+      logTestController_.setDebug<minifi::processors::PutFile::ReadCallback>();
+    }
+
+ protected:
+    void reInitialize() {
+      testController_.reset(new TestController());
+      plan_ = testController_->createPlan();
+    }
+
+    std::string createTempDir() {
+      char dirtemplate[] = "/tmp/gt.XXXXXX";
+      std::string temp_dir = testController_->createTempDirectory(dirtemplate);
+      REQUIRE(!temp_dir.empty());
+      struct stat buffer;
+      REQUIRE(-1 != stat(temp_dir.c_str(), &buffer));
+      REQUIRE(S_ISDIR(buffer.st_mode));
+      return temp_dir;
+    }
+
+    std::string putFileToDir(const std::string& dir_path, const std::string& 
file_name, const std::string& content) {
+      std::string file_path(dir_path + utils::file::FileUtils::get_separator() 
+ file_name);
+      std::ofstream out_file(file_path);
+      if (out_file.is_open()) {
+        out_file << content;
+        out_file.close();
+      }
+      return file_path;
+    }
+
+    std::string createTempDirWithFile(const std::string& file_name, const 
std::string& content) {
+      std::string temp_dir = createTempDir();
+      putFileToDir(temp_dir, file_name, content);
+      return temp_dir;
+    }
+
+    std::string getFileContent(const std::string& file_name) {
+      std::ifstream file_handle(file_name);
+      REQUIRE(file_handle.is_open());
+      const std::string file_content{ 
(std::istreambuf_iterator<char>(file_handle)), 
(std::istreambuf_iterator<char>())};
+      file_handle.close();
+      return file_content;
+    }
+
+    std::string getScriptFullPath(const std::string& script_file_name) {
+      return SCRIPT_FILES_DIRECTORY + utils::file::FileUtils::get_separator() 
+ script_file_name;
+    }
+
+    const std::string TEST_FILE_NAME{ "test_file.txt" };
+    const std::string TEST_FILE_CONTENT{ "Test text\n" };
+    const std::string SCRIPT_FILES_DIRECTORY{ "test_scripts" };

Review comment:
       I think we only need one object of these, not one every instance. They 
should go outside of the class, become `static`, or possibly both (with 
`static` referring to linkage in this case).

##########
File path: libminifi/test/script-tests/ExecutePythonProcessorTests.cpp
##########
@@ -0,0 +1,276 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define CATCH_CONFIG_MAIN
+
+#include <memory>
+#include <string>
+#include <set>
+
+#include "../TestBase.h"
+
+#include "processors/GetFile.h"
+#include "python/ExecutePythonProcessor.h"
+#include "processors/LogAttribute.h"
+#include "processors/PutFile.h"
+#include "utils/file/FileUtils.h"
+
+namespace {
+
+#include <unistd.h>
+#define GetCurrentDir getcwd
+
+std::string GetCurrentWorkingDir(void) {
+  char buff[FILENAME_MAX];
+  GetCurrentDir(buff, FILENAME_MAX);
+  std::string current_working_dir(buff);
+  return current_working_dir;
+}
+
+class ExecutePythonProcessorTestBase {
+ public:
+    ExecutePythonProcessorTestBase() :
+      logTestController_(LogTestController::getInstance()),
+      
logger_(logging::LoggerFactory<org::apache::nifi::minifi::python::processors::ExecutePythonProcessor>::getLogger())
 {
+      reInitialize();
+    }
+    virtual ~ExecutePythonProcessorTestBase() {
+      logTestController_.reset();
+      logTestController_.setDebug<TestPlan>();
+      
logTestController_.setDebug<minifi::python::processors::ExecutePythonProcessor>();
+      logTestController_.setDebug<minifi::processors::PutFile>();
+      logTestController_.setDebug<minifi::processors::PutFile::ReadCallback>();
+    }
+
+ protected:
+    void reInitialize() {
+      testController_.reset(new TestController());
+      plan_ = testController_->createPlan();
+    }
+
+    std::string createTempDir() {
+      char dirtemplate[] = "/tmp/gt.XXXXXX";
+      std::string temp_dir = testController_->createTempDirectory(dirtemplate);
+      REQUIRE(!temp_dir.empty());
+      struct stat buffer;
+      REQUIRE(-1 != stat(temp_dir.c_str(), &buffer));
+      REQUIRE(S_ISDIR(buffer.st_mode));
+      return temp_dir;
+    }
+
+    std::string putFileToDir(const std::string& dir_path, const std::string& 
file_name, const std::string& content) {
+      std::string file_path(dir_path + utils::file::FileUtils::get_separator() 
+ file_name);
+      std::ofstream out_file(file_path);
+      if (out_file.is_open()) {
+        out_file << content;
+        out_file.close();
+      }
+      return file_path;
+    }
+
+    std::string createTempDirWithFile(const std::string& file_name, const 
std::string& content) {
+      std::string temp_dir = createTempDir();
+      putFileToDir(temp_dir, file_name, content);
+      return temp_dir;
+    }
+
+    std::string getFileContent(const std::string& file_name) {
+      std::ifstream file_handle(file_name);
+      REQUIRE(file_handle.is_open());
+      const std::string file_content{ 
(std::istreambuf_iterator<char>(file_handle)), 
(std::istreambuf_iterator<char>())};
+      file_handle.close();
+      return file_content;
+    }
+
+    std::string getScriptFullPath(const std::string& script_file_name) {
+      return SCRIPT_FILES_DIRECTORY + utils::file::FileUtils::get_separator() 
+ script_file_name;
+    }
+
+    const std::string TEST_FILE_NAME{ "test_file.txt" };
+    const std::string TEST_FILE_CONTENT{ "Test text\n" };
+    const std::string SCRIPT_FILES_DIRECTORY{ "test_scripts" };
+
+    std::unique_ptr<TestController> testController_;
+    std::shared_ptr<TestPlan> plan_;
+    LogTestController& logTestController_;
+    std::shared_ptr<logging::Logger> logger_;
+};
+
+class SimplePythonFlowFileTransferTest : public ExecutePythonProcessorTestBase 
{
+ public:
+  enum class Expectation {
+    OUTPUT_FILE_MATCHES_INPUT,
+    RUNTIME_RELATIONSHIP_EXCEPTION,
+    PROCESSOR_INITIALIZATION_EXCEPTION
+  };
+  SimplePythonFlowFileTransferTest() : ExecutePythonProcessorTestBase{} {}
+
+ protected:
+  void testSimpleFilePassthrough(const Expectation expectation, const 
core::Relationship& execute_python_out_conn, const std::string& 
used_as_script_file, const std::string& used_as_script_body) {
+    reInitialize();
+    const std::string input_dir = createTempDirWithFile(TEST_FILE_NAME, 
TEST_FILE_CONTENT);
+    const std::string output_dir = createTempDir();
+
+    addGetFileProcessorToPlan(input_dir);
+    if (Expectation::PROCESSOR_INITIALIZATION_EXCEPTION == expectation) {
+      REQUIRE_THROWS(addExecutePythonProcessorToPlan(used_as_script_file, 
used_as_script_body));
+      return;
+    }
+    REQUIRE_NOTHROW(addExecutePythonProcessorToPlan(used_as_script_file, 
used_as_script_body));
+    addPutFileProcessorToPlan(execute_python_out_conn, output_dir);
+
+    plan_->runNextProcessor();  // GetFile
+    if (Expectation::RUNTIME_RELATIONSHIP_EXCEPTION == expectation) {
+      REQUIRE_THROWS(plan_->runNextProcessor());  // ExecutePythonProcessor
+      return;
+    }
+    REQUIRE_NOTHROW(plan_->runNextProcessor());  // ExecutePythonProcessor
+    plan_->runNextProcessor();  // PutFile
+
+    const std::string output_file_path = output_dir + 
utils::file::FileUtils::get_separator() +  TEST_FILE_NAME;
+
+    if (Expectation::OUTPUT_FILE_MATCHES_INPUT == expectation) {
+      const std::string output_file_content{ getFileContent(output_file_path) 
};
+      REQUIRE(TEST_FILE_CONTENT == output_file_content);
+    }
+  }
+  void testsStatefulProcessor() {
+    reInitialize();
+    const std::string output_dir = createTempDir();
+
+    auto executePythonProcessor = 
plan_->addProcessor("ExecutePythonProcessor", "executePythonProcessor");
+    plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptFile.getName(),
 getScriptFullPath("stateful_processor.py"));
+    executePythonProcessor -> initialize();
+
+    addPutFileProcessorToPlan(core::Relationship("success", "description"), 
output_dir);
+    plan_->runNextProcessor();  // ExecutePythonProcessor
+    for (std::size_t i = 0; i < 10; ++i) {
+      plan_->runCurrentProcessor();  // ExecutePythonProcessor
+    }
+    plan_->runNextProcessor();  // PutFile
+    for (std::size_t i = 0; i < 10; ++i) {
+      plan_->runCurrentProcessor();  // PutFile
+      const std::string state_name = std::to_string(i);
+      const std::string output_file_path = output_dir + 
utils::file::FileUtils::get_separator() + state_name;
+      const std::string output_file_content{ getFileContent(output_file_path) 
};
+      REQUIRE(output_file_content == state_name);
+    }
+  }
+
+ private:
+  std::shared_ptr<core::Processor> addGetFileProcessorToPlan(const 
std::string& dir_path) {
+    std::shared_ptr<core::Processor> getfile = plan_->addProcessor("GetFile", 
"getfileCreate2");
+    plan_->setProperty(getfile, 
org::apache::nifi::minifi::processors::GetFile::Directory.getName(), dir_path);
+    plan_->setProperty(getfile, 
org::apache::nifi::minifi::processors::GetFile::KeepSourceFile.getName(), 
"true");
+    return getfile;
+  }
+
+  std::shared_ptr<core::Processor> addExecutePythonProcessorToPlan(const 
std::string& used_as_script_file, const std::string& used_as_script_body) {
+    auto executePythonProcessor = 
plan_->addProcessor("ExecutePythonProcessor", "executePythonProcessor", 
core::Relationship("success", "description"), true);
+    if ("" != used_as_script_file) {
+      plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptFile.getName(),
 getScriptFullPath(used_as_script_file));
+    }
+    if ("" != used_as_script_body) {
+        plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptBody.getName(),
 getFileContent(getScriptFullPath(used_as_script_body)));
+    }
+    executePythonProcessor -> initialize();
+    return executePythonProcessor;
+  }
+
+  std::shared_ptr<core::Processor> addPutFileProcessorToPlan(const 
core::Relationship& execute_python_outbound_connection, const std::string& 
dir_path) {
+    std::shared_ptr<core::Processor> putfile = plan_->addProcessor("PutFile", 
"putfile", execute_python_outbound_connection, true);
+    plan_->setProperty(putfile, 
org::apache::nifi::minifi::processors::PutFile::Directory.getName(), dir_path);
+    return putfile;
+  }
+};
+
+// Test for python processors for simple passthrough cases
+//
+// +-----------+     +--------------------------+       +-----------+
+// |  Getfile  |   .-+  ExecutePythonProcessor  |     .-+  PutFile  |
+// +-----------+  /  +  -  -  -  -  -  -  -  -  +    /  +-----------+
+// |  success  +-°   |    Attribute: Script     |   /   |  success  +-+ checked
+// +-----------+     +--------------------------+  /    +-----------+
+//                   |         success          +-°
+//                   +--------------------------+
+//                   |         failure          +-X either success or failure 
is hooked up
+//                   +--------------------------+
+//
+// testSimpleFilePassthrough(OUTPUT_FILE_MATCHES_INPUT, SUCCESS, "", 
"passthrough_processor_transfering_to_success.py");
+//
+// translates to
+//
+// GIVEN an ExecutePythonProcessor set up with a "Script Body" attribute that 
transfers to REL_SUCCESS, but not "Script File"
+// WHEN the processor is triggered
+// THEN any consumer using the success relationship as source should receive 
the transfered data
+//
+TEST_CASE_METHOD(SimplePythonFlowFileTransferTest, "Simple file passthrough", 
"[executePythonProcessorSimple]") {
+  // Expectations
+  const auto OUTPUT_FILE_MATCHES_INPUT          = 
SimplePythonFlowFileTransferTest::Expectation::OUTPUT_FILE_MATCHES_INPUT;
+  const auto RUNTIME_RELATIONSHIP_EXCEPTION    = 
SimplePythonFlowFileTransferTest::Expectation::RUNTIME_RELATIONSHIP_EXCEPTION;
+  const auto PROCESSOR_INITIALIZATION_EXCEPTION = 
SimplePythonFlowFileTransferTest::Expectation::PROCESSOR_INITIALIZATION_EXCEPTION;
+  // ExecutePython outbound relationships
+  const core::Relationship SUCCESS {"success", "description"};
+  const core::Relationship FAILURE{"failure", "description"};
+
+  // For the tests "" is threated as none-provided since no optional 
implementation was ported to the project yet
+
+  ////////////////////////////////////////////////////////////
+  // 0. Neither valid script file nor script body provided  //
+  ////////////////////////////////////////////////////////////
+
+  //                                          TEST EXPECTATION  OUT_REL        
USE_AS_SCRIPT_FILE  USE_AS_SCRIPT_BODY
+  testSimpleFilePassthrough(PROCESSOR_INITIALIZATION_EXCEPTION, SUCCESS,       
                "", "");  // NOLINT

Review comment:
       Comment blocks like this are a bad sign IMO. I like the content in this 
case, just not the formatting, because it distracts attention from the code to 
the comment.
   ```suggestion
     // Neither valid script file nor script body provided
     //                                          TEST EXPECTATION  OUT_REL      
  USE_AS_SCRIPT_FILE  USE_AS_SCRIPT_BODY
     testSimpleFilePassthrough(PROCESSOR_INITIALIZATION_EXCEPTION, SUCCESS,     
                  "", "");  // NOLINT
   ```

##########
File path: libminifi/test/script-tests/CMakeLists.txt
##########
@@ -19,6 +19,13 @@
 
 if (NOT DISABLE_PYTHON_SCRIPTING)
        file(GLOB EXECUTESCRIPT_PYTHON_INTEGRATION_TESTS  "Python*.cpp")
+       file(GLOB EXECUTEPYTHONPROCESSOR_UNIT_TESTS  
"ExecutePythonProcessorTests.cpp")
+       file(GLOB PY_SOURCES  "python/*.cpp")
+       find_package(PythonLibs 3.5)
+       if (NOT PYTHONLIBS_FOUND)
+               find_package(PythonLibs 3.0 REQUIRED)
+       endif()

Review comment:
       I think we require python 3.5 on all platforms, so a fallback to 3.0 
doesn't seem to provide any value as far as I understand. The version argument 
of `find_package` takes a minimum required version AFAIK, so the above code is 
equivalent to just `find_package(PythonLibs 3.0 REQUIRED)`.
   
   If my assumptions are correct, we should pull python 3.5.
   ```suggestion
        find_package(PythonLibs 3.5 REQUIRED)
   ```

##########
File path: libminifi/test/script-tests/ExecutePythonProcessorTests.cpp
##########
@@ -0,0 +1,276 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define CATCH_CONFIG_MAIN
+
+#include <memory>
+#include <string>
+#include <set>
+
+#include "../TestBase.h"
+
+#include "processors/GetFile.h"
+#include "python/ExecutePythonProcessor.h"
+#include "processors/LogAttribute.h"
+#include "processors/PutFile.h"
+#include "utils/file/FileUtils.h"
+
+namespace {
+
+#include <unistd.h>
+#define GetCurrentDir getcwd

Review comment:
       Why do we need this macro? Why not just call `getcwd()`?

##########
File path: extensions/script/python/ExecutePythonProcessor.cpp
##########
@@ -46,144 +50,177 @@ core::Relationship 
ExecutePythonProcessor::Failure("failure", "Script failures")
 void ExecutePythonProcessor::initialize() {
   // initialization requires that we do a little leg work prior to onSchedule
   // so that we can provide manifest our processor identity
-  std::set<core::Property> properties;
-
-  std::string prop;
-  getProperty(ScriptFile.getName(), prop);
-
-  properties.insert(ScriptFile);
-  properties.insert(ModuleDirectory);
-  setSupportedProperties(properties);
-
-  std::set<core::Relationship> relationships;
-  relationships.insert(Success);
-  relationships.insert(Failure);
-  setSupportedRelationships(std::move(relationships));
-  setAcceptAllProperties();
-  if (!prop.empty()) {
-    setProperty(ScriptFile, prop);
-    std::shared_ptr<script::ScriptEngine> engine;
-    python_logger_ = 
logging::LoggerFactory<ExecutePythonProcessor>::getAliasedLogger(getName());
+  if (getProperties().empty()) {
+    setSupportedProperties({
+      ScriptFile,
+      ScriptBody,
+      ModuleDirectory
+    });
+    setAcceptAllProperties();
+    setSupportedRelationships({
+      Success,
+      Failure
+    });
+    valid_init_ = false;
+    return;
+  }
 
-    engine = createEngine<python::PythonScriptEngine>();
+  python_logger_ = 
logging::LoggerFactory<ExecutePythonProcessor>::getAliasedLogger(getName());
 
-    if (engine == nullptr) {
-      throw std::runtime_error("No script engine available");
-    }
+  getProperty(ModuleDirectory.getName(), module_directory_);
 
-    try {
-      engine->evalFile(prop);
-      auto me = shared_from_this();
-      triggerDescribe(engine, me);
-      triggerInitialize(engine, me);
+  valid_init_ = false;
+  appendPathForImportModules();
+  loadScript();
+  try {
+    if ("" != script_to_exec_) {

Review comment:
       I think `!script_to_exec_.empty()` (or `not script_to_exec_.empty()`) 
would be more readable.

##########
File path: extensions/script/python/ExecutePythonProcessor.cpp
##########
@@ -46,144 +50,177 @@ core::Relationship 
ExecutePythonProcessor::Failure("failure", "Script failures")
 void ExecutePythonProcessor::initialize() {
   // initialization requires that we do a little leg work prior to onSchedule
   // so that we can provide manifest our processor identity
-  std::set<core::Property> properties;
-
-  std::string prop;
-  getProperty(ScriptFile.getName(), prop);
-
-  properties.insert(ScriptFile);
-  properties.insert(ModuleDirectory);
-  setSupportedProperties(properties);
-
-  std::set<core::Relationship> relationships;
-  relationships.insert(Success);
-  relationships.insert(Failure);
-  setSupportedRelationships(std::move(relationships));
-  setAcceptAllProperties();
-  if (!prop.empty()) {
-    setProperty(ScriptFile, prop);
-    std::shared_ptr<script::ScriptEngine> engine;
-    python_logger_ = 
logging::LoggerFactory<ExecutePythonProcessor>::getAliasedLogger(getName());
+  if (getProperties().empty()) {
+    setSupportedProperties({
+      ScriptFile,
+      ScriptBody,
+      ModuleDirectory
+    });
+    setAcceptAllProperties();
+    setSupportedRelationships({
+      Success,
+      Failure
+    });
+    valid_init_ = false;
+    return;
+  }
 
-    engine = createEngine<python::PythonScriptEngine>();
+  python_logger_ = 
logging::LoggerFactory<ExecutePythonProcessor>::getAliasedLogger(getName());
 
-    if (engine == nullptr) {
-      throw std::runtime_error("No script engine available");
-    }
+  getProperty(ModuleDirectory.getName(), module_directory_);
 
-    try {
-      engine->evalFile(prop);
-      auto me = shared_from_this();
-      triggerDescribe(engine, me);
-      triggerInitialize(engine, me);
+  valid_init_ = false;
+  appendPathForImportModules();
+  loadScript();
+  try {
+    if ("" != script_to_exec_) {
+      std::shared_ptr<python::PythonScriptEngine> engine = getScriptEngine();
+      engine->eval(script_to_exec_);
+      auto shared_this = shared_from_this();
+      engine->describe(shared_this);
+      engine->onInitialize(shared_this);
+      handleEngineNoLongerInUse(std::move(engine));
       valid_init_ = true;
-    } catch (std::exception &exception) {
-      logger_->log_error("Caught Exception %s", exception.what());
-      engine = nullptr;
-      std::rethrow_exception(std::current_exception());
-      valid_init_ = false;
-    } catch (...) {
-      logger_->log_error("Caught Exception");
-      engine = nullptr;
-      std::rethrow_exception(std::current_exception());
-      valid_init_ = false;
     }
-
+  }
+  catch (const std::exception& exception) {
+    logger_->log_error("Caught Exception: %s", exception.what());
+    std::rethrow_exception(std::current_exception());
+  }
+  catch (...) {
+    logger_->log_error("Caught Exception");
+    std::rethrow_exception(std::current_exception());
   }
 }
 
 void ExecutePythonProcessor::onSchedule(const 
std::shared_ptr<core::ProcessContext> &context, const 
std::shared_ptr<core::ProcessSessionFactory> &sessionFactory) {
   if (!valid_init_) {
-    throw std::runtime_error("Could not correctly in initialize " + getName());
-  }
-  context->getProperty(ScriptFile.getName(), script_file_);
-  context->getProperty(ModuleDirectory.getName(), module_directory_);
-  if (script_file_.empty() && script_engine_.empty()) {
-    logger_->log_error("Script File must be defined");
-    return;
+    throw std::runtime_error("Could not correctly initialize " + getName());
   }
-
   try {
-    std::shared_ptr<script::ScriptEngine> engine;
-
-    // Use an existing engine, if one is available
-    if (script_engine_q_.try_dequeue(engine)) {
-      logger_->log_debug("Using available %s script engine instance", 
script_engine_);
-    } else {
-      logger_->log_info("Creating new %s script instance", script_engine_);
-      logger_->log_info("Approximately %d %s script instances created for this 
processor", script_engine_q_.size_approx(), script_engine_);
-
-      engine = createEngine<python::PythonScriptEngine>();
-
-      if (engine == nullptr) {
-        throw std::runtime_error("No script engine available");
-      }
-
-      if (!script_file_.empty()) {
-        engine->evalFile(script_file_);
-      } else {
-        throw std::runtime_error("No Script File is available to execute");
-      }
+    // TODO(hunyadi): When using "Script File" property, we currently re-read 
the script file content every time the processor is on schedule. This should 
change to single-read when we release 1.0.0
+    // https://issues.apache.org/jira/browse/MINIFICPP-1223
+    reloadScriptIfUsingScriptFileProperty();
+    if (script_to_exec_.empty()) {
+      throw std::runtime_error("Neither Script Body nor Script File is 
available to execute");
     }
+    std::shared_ptr<python::PythonScriptEngine> engine = getScriptEngine();
 
-    triggerSchedule(engine, context);
+    engine->eval(script_to_exec_);
+    engine->onSchedule(context);
 
-    // Make engine available for use again
-    if (script_engine_q_.size_approx() < getMaxConcurrentTasks()) {
-      logger_->log_debug("Releasing %s script engine", script_engine_);
-      script_engine_q_.enqueue(engine);
-    } else {
-      logger_->log_info("Destroying script engine because it is no longer 
needed");
-    }
-  } catch (std::exception &exception) {
-    logger_->log_error("Caught Exception %s", exception.what());
-  } catch (...) {
+    handleEngineNoLongerInUse(std::move(engine));
+  }
+  catch (const std::exception& exception) {
+    logger_->log_error("Caught Exception: %s", exception.what());
+  }
+  catch (...) {
     logger_->log_error("Caught Exception");
   }
 }
 
 void ExecutePythonProcessor::onTrigger(const 
std::shared_ptr<core::ProcessContext> &context, const 
std::shared_ptr<core::ProcessSession> &session) {
+  if (!valid_init_) {
+    throw std::runtime_error("Could not correctly initialize " + getName());
+  }
   try {
-    std::shared_ptr<script::ScriptEngine> engine;
-
-    // Use an existing engine, if one is available
-    if (script_engine_q_.try_dequeue(engine)) {
-      logger_->log_debug("Using available %s script engine instance", 
script_engine_);
-    } else {
-      logger_->log_info("Creating new %s script instance", script_engine_);
-      logger_->log_info("Approximately %d %s script instances created for this 
processor", script_engine_q_.size_approx(), script_engine_);
-
-      engine = createEngine<python::PythonScriptEngine>();
-
-      if (engine == nullptr) {
-        throw std::runtime_error("No script engine available");
-      }
-
-      if (!script_file_.empty()) {
-        engine->evalFile(script_file_);
-      } else {
-        throw std::runtime_error("No Script File is available to execute");
-      }
+    // TODO(hunyadi): When using "Script File" property, we currently re-read 
the script file content every time the processor is on schedule. This should 
change to single-read when we release 1.0.0
+    // https://issues.apache.org/jira/browse/MINIFICPP-1223
+    reloadScriptIfUsingScriptFileProperty();
+    if (script_to_exec_.empty()) {
+      throw std::runtime_error("Neither Script Body nor Script File is 
available to execute");
     }
 
-    triggerEngineProcessor(engine, context, session);
-
-    // Make engine available for use again
-    if (script_engine_q_.size_approx() < getMaxConcurrentTasks()) {
-      logger_->log_debug("Releasing %s script engine", script_engine_);
-      script_engine_q_.enqueue(engine);
-    } else {
-      logger_->log_info("Destroying script engine because it is no longer 
needed");
-    }
-  } catch (std::exception &exception) {
-    logger_->log_error("Caught Exception %s", exception.what());
+    std::shared_ptr<python::PythonScriptEngine> engine = getScriptEngine();
+    engine->onTrigger(context, session);
+    handleEngineNoLongerInUse(std::move(engine));
+  }
+  catch (const std::exception &exception) {
+    logger_->log_error("Caught Exception: %s", exception.what());
     this->yield();
-  } catch (...) {
+  }
+  catch (...) {
     logger_->log_error("Caught Exception");
     this->yield();
   }
 }
 
+// TODO(hunyadi): This is potentially not what we want. See 
https://issues.apache.org/jira/browse/MINIFICPP-1222
+std::shared_ptr<python::PythonScriptEngine> 
ExecutePythonProcessor::getScriptEngine() {
+  std::shared_ptr<python::PythonScriptEngine> engine;
+  // Use an existing engine, if one is available
+  if (script_engine_q_.try_dequeue(engine)) {
+    logger_->log_debug("Using available [%p] script engine instance", 
engine.get());
+    return engine;
+  }
+  engine = createEngine<python::PythonScriptEngine>();
+  logger_->log_info("Created new [%p] script instance", engine.get());
+  logger_->log_info("Approximately %d script instances created for this 
processor", script_engine_q_.size_approx());
+  if (engine == nullptr) {
+    throw std::runtime_error("No script engine available");
+  }
+  return engine;
+}
+
+void 
ExecutePythonProcessor::handleEngineNoLongerInUse(std::shared_ptr<python::PythonScriptEngine>&&
 engine) {
+  // Make engine available for use again
+  if (script_engine_q_.size_approx() < getMaxConcurrentTasks()) {
+    logger_->log_debug("Releasing [%p] script engine", engine.get());
+    script_engine_q_.enqueue(engine);
+  } else {
+    logger_->log_info("Destroying script engine because it is no longer 
needed");
+  }
+}
+
+void ExecutePythonProcessor::appendPathForImportModules() {
+  // TODO(hunyadi): I have spent some time trying to figure out pybind11, but
+  // could not get this working yet. It is up to be implemented later
+  // https://issues.apache.org/jira/browse/MINIFICPP-1224
+  if ("" != module_directory_) {
+    logger_ -> log_error("Not supported property: Module Directory.");
+  }
+
+}
+
+void ExecutePythonProcessor::loadScriptFromFile(const std::string& file_path) {
+  std::ifstream file_handle(file_path);
+  if (!file_handle.is_open()) {
+    script_to_exec_ = "";
+    throw std::runtime_error("Failed to read Script File: " + file_path);
+  }
+  script_to_exec_ = std::string{ 
(std::istreambuf_iterator<char>(file_handle)), 
(std::istreambuf_iterator<char>())};
+  file_handle.close();

Review comment:
       In the `script_to_exec_` assignment line, spacing inside `{}`s are 
inconsistent. Either use spaces on both sides or neither, IMO.
   
   `close()` at the end of the block is redundant: the dtor will close the file 
anyway.

##########
File path: libminifi/test/script-tests/ExecutePythonProcessorTests.cpp
##########
@@ -0,0 +1,276 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define CATCH_CONFIG_MAIN
+
+#include <memory>
+#include <string>
+#include <set>
+
+#include "../TestBase.h"
+
+#include "processors/GetFile.h"
+#include "python/ExecutePythonProcessor.h"
+#include "processors/LogAttribute.h"
+#include "processors/PutFile.h"
+#include "utils/file/FileUtils.h"
+
+namespace {
+
+#include <unistd.h>
+#define GetCurrentDir getcwd
+
+std::string GetCurrentWorkingDir(void) {
+  char buff[FILENAME_MAX];
+  GetCurrentDir(buff, FILENAME_MAX);
+  std::string current_working_dir(buff);
+  return current_working_dir;
+}
+
+class ExecutePythonProcessorTestBase {
+ public:
+    ExecutePythonProcessorTestBase() :
+      logTestController_(LogTestController::getInstance()),
+      
logger_(logging::LoggerFactory<org::apache::nifi::minifi::python::processors::ExecutePythonProcessor>::getLogger())
 {
+      reInitialize();
+    }
+    virtual ~ExecutePythonProcessorTestBase() {
+      logTestController_.reset();
+      logTestController_.setDebug<TestPlan>();
+      
logTestController_.setDebug<minifi::python::processors::ExecutePythonProcessor>();
+      logTestController_.setDebug<minifi::processors::PutFile>();
+      logTestController_.setDebug<minifi::processors::PutFile::ReadCallback>();
+    }
+
+ protected:
+    void reInitialize() {
+      testController_.reset(new TestController());
+      plan_ = testController_->createPlan();
+    }
+
+    std::string createTempDir() {
+      char dirtemplate[] = "/tmp/gt.XXXXXX";
+      std::string temp_dir = testController_->createTempDirectory(dirtemplate);
+      REQUIRE(!temp_dir.empty());
+      struct stat buffer;
+      REQUIRE(-1 != stat(temp_dir.c_str(), &buffer));
+      REQUIRE(S_ISDIR(buffer.st_mode));
+      return temp_dir;
+    }
+
+    std::string putFileToDir(const std::string& dir_path, const std::string& 
file_name, const std::string& content) {
+      std::string file_path(dir_path + utils::file::FileUtils::get_separator() 
+ file_name);
+      std::ofstream out_file(file_path);
+      if (out_file.is_open()) {
+        out_file << content;
+        out_file.close();
+      }
+      return file_path;
+    }
+
+    std::string createTempDirWithFile(const std::string& file_name, const 
std::string& content) {
+      std::string temp_dir = createTempDir();
+      putFileToDir(temp_dir, file_name, content);
+      return temp_dir;
+    }
+
+    std::string getFileContent(const std::string& file_name) {
+      std::ifstream file_handle(file_name);
+      REQUIRE(file_handle.is_open());
+      const std::string file_content{ 
(std::istreambuf_iterator<char>(file_handle)), 
(std::istreambuf_iterator<char>())};
+      file_handle.close();
+      return file_content;
+    }

Review comment:
       These are generic enough that they could go to `FileUtils` IMO.
   
   I'd remove the `std::ifstream::close` calls because they are both right 
before `return`, after which the file is closed anyway. They don't hurt but 
they're not needed either.
   
   If we handle errors in some way, we shouldn't ignore them IMO. I mean if we 
check for a good file stream, we should throw if it's not good.

##########
File path: libminifi/test/script-tests/ExecutePythonProcessorTests.cpp
##########
@@ -0,0 +1,276 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define CATCH_CONFIG_MAIN
+
+#include <memory>
+#include <string>
+#include <set>
+
+#include "../TestBase.h"
+
+#include "processors/GetFile.h"
+#include "python/ExecutePythonProcessor.h"
+#include "processors/LogAttribute.h"
+#include "processors/PutFile.h"
+#include "utils/file/FileUtils.h"
+
+namespace {
+
+#include <unistd.h>
+#define GetCurrentDir getcwd
+
+std::string GetCurrentWorkingDir(void) {
+  char buff[FILENAME_MAX];
+  GetCurrentDir(buff, FILENAME_MAX);
+  std::string current_working_dir(buff);
+  return current_working_dir;
+}
+
+class ExecutePythonProcessorTestBase {
+ public:
+    ExecutePythonProcessorTestBase() :
+      logTestController_(LogTestController::getInstance()),
+      
logger_(logging::LoggerFactory<org::apache::nifi::minifi::python::processors::ExecutePythonProcessor>::getLogger())
 {
+      reInitialize();
+    }
+    virtual ~ExecutePythonProcessorTestBase() {
+      logTestController_.reset();
+      logTestController_.setDebug<TestPlan>();
+      
logTestController_.setDebug<minifi::python::processors::ExecutePythonProcessor>();
+      logTestController_.setDebug<minifi::processors::PutFile>();
+      logTestController_.setDebug<minifi::processors::PutFile::ReadCallback>();
+    }
+
+ protected:
+    void reInitialize() {
+      testController_.reset(new TestController());
+      plan_ = testController_->createPlan();
+    }
+
+    std::string createTempDir() {
+      char dirtemplate[] = "/tmp/gt.XXXXXX";
+      std::string temp_dir = testController_->createTempDirectory(dirtemplate);
+      REQUIRE(!temp_dir.empty());
+      struct stat buffer;
+      REQUIRE(-1 != stat(temp_dir.c_str(), &buffer));
+      REQUIRE(S_ISDIR(buffer.st_mode));
+      return temp_dir;
+    }
+
+    std::string putFileToDir(const std::string& dir_path, const std::string& 
file_name, const std::string& content) {
+      std::string file_path(dir_path + utils::file::FileUtils::get_separator() 
+ file_name);
+      std::ofstream out_file(file_path);
+      if (out_file.is_open()) {
+        out_file << content;
+        out_file.close();
+      }
+      return file_path;
+    }
+
+    std::string createTempDirWithFile(const std::string& file_name, const 
std::string& content) {
+      std::string temp_dir = createTempDir();
+      putFileToDir(temp_dir, file_name, content);
+      return temp_dir;
+    }
+
+    std::string getFileContent(const std::string& file_name) {
+      std::ifstream file_handle(file_name);
+      REQUIRE(file_handle.is_open());
+      const std::string file_content{ 
(std::istreambuf_iterator<char>(file_handle)), 
(std::istreambuf_iterator<char>())};
+      file_handle.close();
+      return file_content;
+    }
+
+    std::string getScriptFullPath(const std::string& script_file_name) {
+      return SCRIPT_FILES_DIRECTORY + utils::file::FileUtils::get_separator() 
+ script_file_name;
+    }
+
+    const std::string TEST_FILE_NAME{ "test_file.txt" };
+    const std::string TEST_FILE_CONTENT{ "Test text\n" };
+    const std::string SCRIPT_FILES_DIRECTORY{ "test_scripts" };
+
+    std::unique_ptr<TestController> testController_;
+    std::shared_ptr<TestPlan> plan_;
+    LogTestController& logTestController_;
+    std::shared_ptr<logging::Logger> logger_;
+};
+
+class SimplePythonFlowFileTransferTest : public ExecutePythonProcessorTestBase 
{
+ public:
+  enum class Expectation {
+    OUTPUT_FILE_MATCHES_INPUT,
+    RUNTIME_RELATIONSHIP_EXCEPTION,
+    PROCESSOR_INITIALIZATION_EXCEPTION
+  };
+  SimplePythonFlowFileTransferTest() : ExecutePythonProcessorTestBase{} {}
+
+ protected:
+  void testSimpleFilePassthrough(const Expectation expectation, const 
core::Relationship& execute_python_out_conn, const std::string& 
used_as_script_file, const std::string& used_as_script_body) {
+    reInitialize();
+    const std::string input_dir = createTempDirWithFile(TEST_FILE_NAME, 
TEST_FILE_CONTENT);
+    const std::string output_dir = createTempDir();
+
+    addGetFileProcessorToPlan(input_dir);
+    if (Expectation::PROCESSOR_INITIALIZATION_EXCEPTION == expectation) {
+      REQUIRE_THROWS(addExecutePythonProcessorToPlan(used_as_script_file, 
used_as_script_body));
+      return;
+    }
+    REQUIRE_NOTHROW(addExecutePythonProcessorToPlan(used_as_script_file, 
used_as_script_body));
+    addPutFileProcessorToPlan(execute_python_out_conn, output_dir);
+
+    plan_->runNextProcessor();  // GetFile
+    if (Expectation::RUNTIME_RELATIONSHIP_EXCEPTION == expectation) {
+      REQUIRE_THROWS(plan_->runNextProcessor());  // ExecutePythonProcessor
+      return;
+    }
+    REQUIRE_NOTHROW(plan_->runNextProcessor());  // ExecutePythonProcessor
+    plan_->runNextProcessor();  // PutFile
+
+    const std::string output_file_path = output_dir + 
utils::file::FileUtils::get_separator() +  TEST_FILE_NAME;
+
+    if (Expectation::OUTPUT_FILE_MATCHES_INPUT == expectation) {
+      const std::string output_file_content{ getFileContent(output_file_path) 
};
+      REQUIRE(TEST_FILE_CONTENT == output_file_content);
+    }
+  }
+  void testsStatefulProcessor() {
+    reInitialize();
+    const std::string output_dir = createTempDir();
+
+    auto executePythonProcessor = 
plan_->addProcessor("ExecutePythonProcessor", "executePythonProcessor");
+    plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptFile.getName(),
 getScriptFullPath("stateful_processor.py"));
+    executePythonProcessor -> initialize();
+
+    addPutFileProcessorToPlan(core::Relationship("success", "description"), 
output_dir);
+    plan_->runNextProcessor();  // ExecutePythonProcessor
+    for (std::size_t i = 0; i < 10; ++i) {
+      plan_->runCurrentProcessor();  // ExecutePythonProcessor
+    }
+    plan_->runNextProcessor();  // PutFile
+    for (std::size_t i = 0; i < 10; ++i) {
+      plan_->runCurrentProcessor();  // PutFile
+      const std::string state_name = std::to_string(i);
+      const std::string output_file_path = output_dir + 
utils::file::FileUtils::get_separator() + state_name;
+      const std::string output_file_content{ getFileContent(output_file_path) 
};
+      REQUIRE(output_file_content == state_name);
+    }
+  }
+
+ private:
+  std::shared_ptr<core::Processor> addGetFileProcessorToPlan(const 
std::string& dir_path) {
+    std::shared_ptr<core::Processor> getfile = plan_->addProcessor("GetFile", 
"getfileCreate2");
+    plan_->setProperty(getfile, 
org::apache::nifi::minifi::processors::GetFile::Directory.getName(), dir_path);
+    plan_->setProperty(getfile, 
org::apache::nifi::minifi::processors::GetFile::KeepSourceFile.getName(), 
"true");
+    return getfile;
+  }
+
+  std::shared_ptr<core::Processor> addExecutePythonProcessorToPlan(const 
std::string& used_as_script_file, const std::string& used_as_script_body) {
+    auto executePythonProcessor = 
plan_->addProcessor("ExecutePythonProcessor", "executePythonProcessor", 
core::Relationship("success", "description"), true);
+    if ("" != used_as_script_file) {
+      plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptFile.getName(),
 getScriptFullPath(used_as_script_file));
+    }
+    if ("" != used_as_script_body) {
+        plan_->setProperty(executePythonProcessor, 
org::apache::nifi::minifi::python::processors::ExecutePythonProcessor::ScriptBody.getName(),
 getFileContent(getScriptFullPath(used_as_script_body)));
+    }
+    executePythonProcessor -> initialize();
+    return executePythonProcessor;
+  }
+
+  std::shared_ptr<core::Processor> addPutFileProcessorToPlan(const 
core::Relationship& execute_python_outbound_connection, const std::string& 
dir_path) {
+    std::shared_ptr<core::Processor> putfile = plan_->addProcessor("PutFile", 
"putfile", execute_python_outbound_connection, true);
+    plan_->setProperty(putfile, 
org::apache::nifi::minifi::processors::PutFile::Directory.getName(), dir_path);
+    return putfile;
+  }
+};
+
+// Test for python processors for simple passthrough cases
+//
+// +-----------+     +--------------------------+       +-----------+
+// |  Getfile  |   .-+  ExecutePythonProcessor  |     .-+  PutFile  |
+// +-----------+  /  +  -  -  -  -  -  -  -  -  +    /  +-----------+
+// |  success  +-°   |    Attribute: Script     |   /   |  success  +-+ checked
+// +-----------+     +--------------------------+  /    +-----------+
+//                   |         success          +-°
+//                   +--------------------------+
+//                   |         failure          +-X either success or failure 
is hooked up
+//                   +--------------------------+
+//
+// testSimpleFilePassthrough(OUTPUT_FILE_MATCHES_INPUT, SUCCESS, "", 
"passthrough_processor_transfering_to_success.py");
+//
+// translates to
+//
+// GIVEN an ExecutePythonProcessor set up with a "Script Body" attribute that 
transfers to REL_SUCCESS, but not "Script File"
+// WHEN the processor is triggered
+// THEN any consumer using the success relationship as source should receive 
the transfered data
+//
+TEST_CASE_METHOD(SimplePythonFlowFileTransferTest, "Simple file passthrough", 
"[executePythonProcessorSimple]") {
+  // Expectations
+  const auto OUTPUT_FILE_MATCHES_INPUT          = 
SimplePythonFlowFileTransferTest::Expectation::OUTPUT_FILE_MATCHES_INPUT;
+  const auto RUNTIME_RELATIONSHIP_EXCEPTION    = 
SimplePythonFlowFileTransferTest::Expectation::RUNTIME_RELATIONSHIP_EXCEPTION;
+  const auto PROCESSOR_INITIALIZATION_EXCEPTION = 
SimplePythonFlowFileTransferTest::Expectation::PROCESSOR_INITIALIZATION_EXCEPTION;
+  // ExecutePython outbound relationships
+  const core::Relationship SUCCESS {"success", "description"};
+  const core::Relationship FAILURE{"failure", "description"};
+
+  // For the tests "" is threated as none-provided since no optional 
implementation was ported to the project yet

Review comment:
       typo: s/threated/treated/




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