[issue36658] Py_Initialze() throws error 'unable to load the file system encoding' when calling Py_SetPath with a path to a directory

[Steve Dower]

Steve Dower  added the comment:

Glad to hear it.

Hopefully as we redesign the embedding initialization APIs this kind of problem 
will become easier to solve (it's certainly one of my concerns with the current 
API).

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resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue36658] Py_Initialze() throws error 'unable to load the file system encoding' when calling Py_SetPath with a path to a directory

[RimacV]

RimacV  added the comment:

As you said, I just had to set all paths, when using Py_SetPath. 
>From my side this issue could be closed. 

Thank you! :-)

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components: +Library (Lib) -Windows

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[issue36658] Py_Initialze() throws error 'unable to load the file system encoding' when calling Py_SetPath with a path to a directory

[RimacV]

RimacV  added the comment:

Thanks for your quick response! I will try your suggestion on tuesday and will 
then let you know, if it worked as expected.

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[issue36658] Py_Initialze() throws error 'unable to load the file system encoding' when calling Py_SetPath with a path to a directory

[Steve Dower]

Steve Dower  added the comment:

This is probably a documentation failure more than anything else. We're in the 
middle of redesigning initialization though, so it's good timing to contribute 
this feedback.

The short answer is that you need to make sure Python can find the 
Lib/encodings directory, typically by putting the standard library in sys.path. 
Py_SetPath clears all inferred paths, so you need to specify all the places 
Python should look. (The rules for where Python looks automatically are 
complicated and vary by platform, which is something I'm keen to fix.)

Paths that don't exist are okay, and that's the zip file. You can choose to put 
the stdlib into a zip, and it will be found automatically if you name it the 
default path, but you can also leave it unzipped and reference the directory.

A full walk through on embedding is more than I'm prepared to type on my phone. 
Hopefully that's enough to get you going for now.

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nosy: +vstinner

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[issue36658] Py_Initialze() throws error 'unable to load the file system encoding' when calling Py_SetPath with a path to a directory

[Stéphane Wirtel]

Change by Stéphane Wirtel :


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components: +Windows -Library (Lib)
nosy: +paul.moore, steve.dower, tim.golden, zach.ware

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[issue36658] Py_Initialze() throws error 'unable to load the file system encoding' when calling Py_SetPath with a path to a directory

[RimacV]

New submission from RimacV :

I compiled the source of CPython 3.7.3 myself on Windows with Visual Studio 
2017 together with some packages like e.g numpy. When I start the Python 
Interpreter I am able to import and use numpy. However when I am running the 
same script via the C-API I get an ModuleNotFoundError. 

So the first thing I did, was to check if numpy is in my site-packages 
directory and indeed there is a folder named numpy-1.16.2-py3.7-win-amd64.egg. 
(Makes sense because the python interpreter can find numpy)

The next thing I did was get some information about the sys.path variable 
created when running the script via the C-API. 

# sys.path content 
C:\Work\build\product\python37.zip
C:\Work\build\product\DLLs
C:\Work\build\product\lib
C:\PROGRAM FILES (X86)\MICROSOFT VISUAL 
STUDIO\2017\PROFESSIONAL\COMMON7\IDE\EXTENSIONS\TESTPLATFORM
C:\Users\rvq\AppData\Roaming\Python\Python37\site-packages

Examining the content of sys.path I noticed two things. 

1. 
C:\Work\build\product\python37.zip has the correct path 
'C:\Work\build\product\'. There was just no zip file. All my files and 
directory were unpacked. So I zipped the files to an archive named python37.zip 
and this resolved the import error.

2. C:\Users\rvq\AppData\Roaming\Python\Python37\site-packages is wrong it 
should be C:\Work\build\product\Lib\site-packages but I dont know how this 
wrong path is created. 


The next thing I tried was to use 
Py_SetPath(L"C:/Work/build/product/Lib/site-packages") before calling 
Py_Initialize(). This led to the 

Fatal Python Error 'unable to load the file system encoding' 
ModuleNotFoundError: No module named 'encodings'


I created a minimal c++ project with exact these two calls and started to debug 
Cpython. 

int main()
{
  Py_SetPath(L"C:/Work/build/product/Lib/site-packages");
  Py_Initialize();
}

I tracked the call of Py_Initialize() down to the call of 

static int
zipimport_zipimporter___init___impl(ZipImporter *self, PyObject *path)

inside of zipimport.c

The comment above this function states the following: 

Create a new zipimporter instance.
'archivepath' must be a path-like object to a zipfile, or to a specific path
inside a zipfile. For example, it can be '/tmp/myimport.zip', or
'/tmp/myimport.zip/mydirectory', if mydirectory is a valid directory inside
the archive.
'ZipImportError' is raised if 'archivepath' doesn't point to a valid Zip
archive.
The 'archive' attribute of the zipimporter object contains the name of the
zipfile targeted.


So for me it seems that the C-API expects the path set with Py_SetPath to be a 
path to a zipfile. Is this expected behaviour or is it a bug? 
If it is not a bug is there a way to changes this so that it can also detect 
directories? 

PS: The ModuleNotFoundError did not occur for me when using Python 3.5.2+, 
which was the version I used in my project before. I also checked if I had set 
any PYTHONHOME or PYTHONPATH environment variables but I did not see one of 
them on my system.

--
components: Library (Lib)
files: Capture.PNG
messages: 340494
nosy: rvq
priority: normal
severity: normal
status: open
title: Py_Initialze() throws error 'unable to load the file system encoding' 
when calling Py_SetPath with a path to a directory
type: behavior
versions: Python 3.7
Added file: https://bugs.python.org/file48274/Capture.PNG

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