FileNotFoundException raised by subprocess.call

[GeoffreyRoyer]

BPO	24888
Nosy	@bitdancer, @ambv, @miss-islington, @iritkatriel, @DonnaDia
PRs	bpo-24888: Clarify subprocess.check_call propagates exceptions if unable to start process #28018 [3.9] bpo-24888: Clarify subprocess.check_call propagates exceptions if unable to start process (GH-28018) #28223 [3.10] bpo-24888: Clarify subprocess.check_call propagates exceptions if unable to start process (GH-28018) #28224

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-09-07.18:45:06.138>
created_at = <Date 2015-08-18.14:36:31.218>
labels = ['easy', 'type-bug', 'docs']
title = 'FileNotFoundException raised by subprocess.call'
updated_at = <Date 2021-09-07.18:45:06.137>
user = 'https://bugs.python.org/GeoffreyRoyer'

bugs.python.org fields:

activity = <Date 2021-09-07.18:45:06.137>
actor = 'lukasz.langa'
assignee = 'docs@python'
closed = True
closed_date = <Date 2021-09-07.18:45:06.138>
closer = 'lukasz.langa'
components = ['Documentation']
creation = <Date 2015-08-18.14:36:31.218>
creator = 'Geoffrey Royer'
dependencies = []
files = []
hgrepos = []
issue_num = 24888
keywords = ['patch', 'easy']
message_count = 11.0
messages = ['248773', '248774', '248775', '396107', '396142', '400438', '400518', '401321', '401323', '401324', '401325']
nosy_count = 8.0
nosy_names = ['r.david.murray', 'docs@python', 'lukasz.langa', 'Geoffrey Royer', 'miss-islington', 'iritkatriel', 'DonnaDia', 'padmashreejha717']
pr_nums = ['28018', '28223', '28224']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue24888'
versions = []

[GeoffreyRoyer]

According to the documentation of the subprocess.check_call function: https://docs.python.org/3/library/subprocess.html#subprocess.check_call

It would be nice to notify the reader that this function can raise FileNotFoundException. It is raised in case when the binary one wants to call does not exist.

Example:

Python 3.4.0 (default, Jun 19 2015, 14:20:21) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import subprocess
>>> subprocess.check_call(["foo", "bar"])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.4/subprocess.py", line 552, in check_call
    retcode = call(*popenargs, **kwargs)
  File "/usr/lib/python3.4/subprocess.py", line 533, in call
    with Popen(*popenargs, **kwargs) as p:
  File "/usr/lib/python3.4/subprocess.py", line 848, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.4/subprocess.py", line 1446, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'foo'

[bitdancer]

We don't in general document all the exceptions that can be raised by a piece of code. This could be an edge case, though. Let's see what others thing.

[bitdancer]

think.

[iritkatriel]

The FileNotFoundException exception is coming from the Popen call, and the docs for subprocess.check_call already mention that it delegates to Popen.

There are quite a few different exceptions that Popen could raise, so I think David's general comment is valid, it would not make sense to mention just this one, or to try and list all of them.

[iritkatriel]

That said, the current wording does seem to imply that only CalledProcessErrors can be raised by this function so it might be worth clarifying that other exceptions can occur if the command could not run at all (without enumerating the precise exceptions).

[DonnaDia]

Hi, I will work on this. I will create a pull request within 3 days.

[padmashreejha717]

You have to add shell=True to execute a shell command. check_output is trying to find an executable. Try this

[ambv]

New changeset 19a304b by DonnaDia in branch 'main':
bpo-24888: Clarify subprocess.check_call propagates exceptions if unable to start process (GH-28018)
19a304b

[ambv]

New changeset 2363910 by Miss Islington (bot) in branch '3.9':
bpo-24888: Clarify subprocess.check_call propagates exceptions if unable to start process (GH-28018) (GH-28223)
2363910

[miss-islington]

New changeset 31be544 by Miss Islington (bot) in branch '3.10':
bpo-24888: Clarify subprocess.check_call propagates exceptions if unable to start process (GH-28018)
31be544

[ambv]

Thanks for the patch, DonnaDia! ✨ 🍰 ✨