Issue 34886: subprocess.run throws exception when input and stdin are passed as kwargs

If input and stdin parameters are passed as keyword arguments to subprocess.run, an exception is thrown even if input and stdin are both None.

The exception is ValueError: stdin and input arguments may not both be used.

I attach a minimal working example of the bug

What is wrong with this?

subprocess.run('ls', input=b'', stdin=None) # this is ok

kwargs = {'input': b'', 'stdin': None}
subprocess.run('ls', **kwargs) # this throws exception

The two calls should have the same behaviour, but one throws exception and the other doesn't. I think the exception shouldn't be thrown, because stdin is None.

I just tried:

    subprocess.run('ls', input=b'', stdin=None)

and I got the same ValueError as for passing using kwargs. Where did you get the idea subprocess.run('ls', input=b'', stdin=None) worked?

The actual code receives input by name, but stdin is received in **kwargs. The test is just:

    if input is not None:
        if 'stdin' in kwargs:
            raise ValueError(...)
        kwargs['stdin'] = PIPE

Perhaps just change `if 'stdin' in kwargs:` to:

    if kwargs.get('stdin') is not None:

so it obeys the documented API (that says stdin defaults to None, and therefore passing stdin=None explicitly should be equivalent to not passing it at all)?

> and I got the same ValueError as for passing using kwargs. Where did you get the idea subprocess.run('ls', input=b'', stdin=None) worked?

Sorry, the example was wrong. Both calls have the same behaviour.

> so it obeys the documented API (that says stdin defaults to None, and therefore passing stdin=None explicitly should be equivalent to not passing it at all)?

The actual problem is this. The fix you propose works for me.

I opened a PR with @josh.r proposed change.

New changeset 8cc605acdda5aff250ab4c9b524a7560f90ca9f3 by Gregory P. Smith (Rémi Lapeyre) in branch 'master':
bpo-34886: Fix subprocess.run handling of exclusive arguments (GH-11727)
https://github.com/python/cpython/commit/8cc605acdda5aff250ab4c9b524a7560f90ca9f3

New changeset 6324ac1293b2cf71559869b88f89f510f9a62a8e by Miss Islington (bot) in branch '3.8':
bpo-34886: Fix subprocess.run handling of exclusive arguments (GH-11727)
https://github.com/python/cpython/commit/6324ac1293b2cf71559869b88f89f510f9a62a8e

New changeset 10b4fd98142edef6ab7b034e10ae5c9551043999 by Miss Islington (bot) in branch '3.7':
bpo-34886: Fix subprocess.run handling of exclusive arguments (GH-11727)
https://github.com/python/cpython/commit/10b4fd98142edef6ab7b034e10ae5c9551043999

thanks!

assignee: gregory.p.smith
versions: + Python 3.8, Python 3.9
keywords: patch, patch, patch
resolution: fixed
messages: + msg345179
stage: patch review -> commit review