[issue43334] venv does not install libpython

[Petr Viktorin]

Petr Viktorin  added the comment:

A venv does *not* create a replica of a python installation directory. Files 
shared with the main Python installation are not copied nor linked. This goes 
for the standard library, as well as the libraries and headers.
(*Executables* are an exception; they're copied, since a venv needs them on the 
PATH.)

Copies would take up unnecessary space, and not all operating systems support 
symbolic links (and we don't want another platform-specific difference), so the 
shared files are only referenced using pyvenv.cfg


If you point to the macros you're using, I can take a look at how they could be 
improved.

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nosy: +petr.viktorin
status: open -> closed

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[issue43334] venv does not install libpython

[Christian Heimes]

Christian Heimes  added the comment:

This sounds like a bug in CMake or Make. Are you using any CMake plugins or 
autoconf/automake macros? It's very well possible that the author of these 
extension made a wrong assumption or the extension was written before venvs 
were introduced.

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[issue43334] venv does not install libpython

[Anup Parikh]

Anup Parikh  added the comment:

I'm seeing this issue in a third-party package that uses CMake and Make based 
build systems rather then setuptools (it's a mostly C library which 
additionally provides some python wrappers). Those build systems can normally 
parse a python installation with the standard directory structure to find the 
library and headers, but fail on a venv. I can bring this up with the package 
developers, but I don't see any downsides to linking the headers/libraries in 
the venv to make it easy to use.

Regarding the comment that venv's are primarily for runtime, I didn't see 
anything in PEP 405 that supports that statement. And in any case, even for 
runtime environments, installing a python package from a source distribution is 
valid, right? So shouldn't the venv support building extensions?

Again, I agree that third party packages that provide python wrappers should 
probably use standard tools (i.e., setuptools) to build the python C 
extensions, but I fail to see the downsides to including links to the 
headers/libraries in the venv for ease of use.

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status: closed -> open

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[issue43334] venv does not install libpython

[Christian Heimes]

Christian Heimes  added the comment:

I agree with Vinay. venvs don't contain copies of libpython or header files by 
design. setuptools will pcik them up from the main installation.

If you have any issues with compiling C extensions, please report them with 
setuptools at https://github.com/pypa/setuptools/

--
nosy: +christian.heimes
resolution:  -> not a bug
stage:  -> resolved
status: pending -> closed

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[issue43334] venv does not install libpython

[Vinay Sajip]

Vinay Sajip  added the comment:

This is not a bug - venvs are primarily *run*-time (as opposed to 
development-time) environments, into which you install pre-built Python 
packages (including ones with C extensions). Can you give a specific example 
where creating a venv and installing packages into it leads to a problem due to 
libpython.XXX being unavailable, with a series of steps to reproduce? If not, 
this issue will need to be closed.

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status: open -> pending

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[issue43334] venv does not install libpython

[Ned Deily]

Change by Ned Deily :


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nosy: +vinay.sajip

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[issue43334] venv does not install libpython

[Anup Parikh]

Anup Parikh  added the comment:

Also, at least on windows, the C-API header files are also missing from the venv

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[issue43334] venv does not install libpython

[Anup Parikh]

Anup Parikh  added the comment:

A typical python installation includes libpython libraries that C extensions 
can link to. Creating virtual environments with venv normally creates a replica 
of a python installation directory, including all the built in python modules. 
However, it doesn't seem to copy over the libpython libraries, so C extensions 
built with a venv activated can't seem to find the libpython (.so, .a, .dll) 
file to link against.

For example, compare the installation directory of python with the venv 
directory. The libpython .so/.a/.dll files are missing in the venv

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[issue43334] venv does not install libpython

[Hasan]

Hasan  added the comment:

Can you please provide more information about this behavior?

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nosy: +AliyevH

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[issue43334] venv does not install libpython

[Anup Parikh]

New submission from Anup Parikh :

The libpython.a or libpython.so objects are not copied/linked in new virtual 
environments when created with venv.

--
components: C API, Installation, Library (Lib)
messages: 387752
nosy: anuppari
priority: normal
severity: normal
status: open
title: venv does not install libpython
type: behavior

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