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[3.13] gh-153970: Fix str() of CalledProcessError when returncode is not an integer (GH-153971) #155931

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[3.13] gh-153970: Fix str() of CalledProcessError when returncode is not an integer (GH-153971) #155931

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4 changes: 2 additions & 2 deletions Doc/library/subprocess.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -239,8 +239,8 @@ underlying :class:`Popen` interface can be used directly.

.. attribute:: returncode

Exit status of the child process. If the process exited due to a
signal, this will be the negative signal number.
Exit status of the child process, an integer. If the process
exited due to a signal, this will be the negative signal number.

.. attribute:: cmd

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6 changes: 3 additions & 3 deletions Lib/subprocess.py
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Expand Up @@ -143,16 +143,16 @@ def __init__(self, returncode, cmd, output=None, stderr=None):
self.stderr = stderr

def __str__(self):
if self.returncode and self.returncode < 0:
if isinstance(self.returncode, int) and self.returncode < 0:
try:
return "Command '%s' died with %r." % (
self.cmd, signal.Signals(-self.returncode))
except ValueError:
return "Command '%s' died with unknown signal %d." % (
self.cmd, -self.returncode)
else:
return "Command '%s' returned non-zero exit status %d." % (
self.cmd, self.returncode)
return (f"Command '{self.cmd}' returned non-zero "
f"exit status {self.returncode}.")

@property
def stdout(self):
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10 changes: 10 additions & 0 deletions Lib/test/test_subprocess.py
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Expand Up @@ -2414,6 +2414,16 @@ def test_CalledProcessError_str_non_zero(self):
error_string = str(err)
self.assertIn("non-zero exit status 2.", error_string)

# returncode which is not an integer, which happens for example when
# Popen is mocked: str() must not fail
for returncode in (None, "2", 2.5, [2]):
with self.subTest(returncode=returncode):
err = subprocess.CalledProcessError(returncode, "fake cmd")
self.assertEqual(
str(err),
f"Command 'fake cmd' returned non-zero "
f"exit status {returncode}.")

def test_preexec(self):
# DISCLAIMER: Setting environment variables is *not* a good use
# of a preexec_fn. This is merely a test.
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-07-22-12-00-00.gh-issue-153970.Kq7Wn3.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Calling :func:`str` on a :exc:`subprocess.CalledProcessError` no longer
raises :exc:`TypeError` when its :attr:`!returncode` is not an integer, such
as ``None``.
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