mik-laj commented on a change in pull request #10303: URL: https://github.com/apache/airflow/pull/10303#discussion_r469502945
########## File path: docs/packages.rst ########## @@ -0,0 +1,75 @@ + .. 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. + + + +Loading Packages in Python and Airflow +====================================== + +How does Python load packages? +------------------------------ +Python's `sys <https://docs.python.org/3/library/sys.html>`_ package provides key variables and functions that are used +or maintained by the interpreter. One such variable is ``sys.path``. It's a list of directories which is searched by +Python during imports. for example, + +.. code-block:: pycon + + >>> import sys + >>> from pprint import pprint + >>> pprint(sys.path) + ['', + '/home/arch/.pyenv/versions/3.7.4/lib/python37.zip', + '/home/arch/.pyenv/versions/3.7.4/lib/python3.7', + '/home/arch/.pyenv/versions/3.7.4/lib/python3.7/lib-dynload', + '/home/arch/venvs/airflow/lib/python3.7/site-packages'] + +``sys.path`` is initialized during program startup. The first precedence is given to the current directory, +i.e, ``path[0]`` is the directory containing the current script that was used to invoke or an empty string in case +it was an interactive shell. Second precedence is given to the ``PYTHONPATH``, followed by installation-dependent +default paths which is managed by `site <https://docs.python.org/3/library/site.html#module-site>`_ module. + +``sys.path`` can also be modified during a Python session, by simply using append (for example, ``sys.path.append("/path/to/custom/package")``). Python will start searching in the newer paths once they're added. Airflow makes use +of this feature as described in the next section. + + +How does Airflow modify this behavior? +-------------------------------------- +Airflow adds three additional directories to ``sys.path``: + +- ``conf.get('core', 'dags_folder')`` +- ``conf.get('core', 'airflow_home')`` Review comment: ```suggestion - ``conf.get('core', 'airflow_home')/config`` ``` ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
