PyQt-builder does not build Designer plugin in conda environment

[Ivan Sinkarenko]

Hello Phil,


Trying to build PyQt5 from source, I ran into issue, where Qt Designer 
plugin would not be built.

PyQt-builder checks for sysconfig.get_config_vars() information in 
CONFIG_ARGS and LDLIBRARY flags.
However, conda's Python is build statically linking to libpython, and 
they provide libpython.so in addition to that in every environment.

Some pointers could be found here: 
https://github.com/conda-forge/python-feedstock/issues/222#issuecomment-436446961

Python 3.7 used to have --enable-shared configuration flag, but in 
Python 3.9 this is no longer the case.
It seems that it might be affecting the PyQt conda-forge package for 
that reason: https://github.com/conda-forge/pyqt-feedstock/issues/113

To verify:
 > docker run -it continuumio/miniconda3 python -c 'import sysconfig; 
print(sysconfig.get_config_vars("CONFIG_ARGS"))'
 > ... output will not have "--enable-shared" ...

 > docker run -it continuumio/miniconda3 python -c 'import sysconfig; 
print(sysconfig.get_config_vars("LDLIBRARY"))'
 > ['libpython3.9.a']

 > docker run -it continuumio/miniconda3 bash -c 'find /opt/conda -name 
"*libpython*"'
 > /opt/conda/lib/libpython3.9.so.1.0
 > /opt/conda/lib/libpython3.9.so
 > /opt/conda/lib/libpython3.so

PyQt-builder already looks for libpython.so with glob, but only after 
sysconfig assumptions are met.
Bypassing those assumptions solves the problem.

As a side note, in PyQt-builder's code, sysconfig gets imported via 
distutils, while it can be imported directly from the stdlib.
Recent versions of setuptools can get upset when somebody imports 
distutils before them, so it could be useful
to minimize that.


Cheers,
Ivan