allow for passing a custom environment to all subprocess calls

[mherkazandjian]

Hi,

I think it is handy to allow passing a custom environment to pkgconfig.clags or the other calls that
invoke Popen at runtime. This would allow to access .pc files found under different PKG_CONFIG_PATH, filter some, add other paths to .pc files...etc..

This would require adding **kwargs to all the function calls that eventually invoke the _query function.

print(pkgconfig.cflags('python3'))
# >>>  '-I/usr/include/python3.6.m'

import os
custom_env = os.environ.copy()
custom_env['PKG_CONFIG_PATH'] = '/path/to/some/other/libs/prefixes'
print(pkgconfig.cflags('python3', env=custom_env))
# >>>  '-I/path/to/some/other/libs/prefixes/include/python3.6.m'

[matze]

I don't get it. Shouldn't the pkgconfig binary pick that up itself and that whole thing be transparent to the user of the API?

[mherkazandjian]

with the current implementation once an import pkgconfig is done, you will always get the
same values for e.g pkgconfig.cflags('python'). But say I want to get the flags for an installation
of python that is not in PKG_CONFIG_PATH, with the changes I am suggesting it would be possible.
i hope i was able to explain things better :)

[matze]

with the current implementation once an import pkgconfig is done, you will always get the
same values

Yes of course. What I meant is: if I want to change the environment then I would do it where it's the most natural place, i.e. the surrounding shell. So if I do export PKG_CONFIG_PATH=/some/where/else right before calling the Python program all should be good.

[mherkazandjian]

I agree. The problem I am trying to solve is that I have installed several versions of python (2.7.9, 2.7.11, 3.5, 3.6, 3.6.1...) in different prefix paths. Based on these versions I want to be able to ask pkg-config to get the cflags and link flags for a specific version without having to specify the pkg-config say at the shell. So this is more of a multiple configuration management exercise.