New submission from bers <[email protected]>:
It is very easy to use filecmp.cmpfiles incorrectly by passing absolute path
names. This is because
1. the documentations does not say that relative path names have to be passed,
and
2. filecmp.cmpfiles does not issue a warning when absolute path names are
passed.
Consider this example code, which does look sensible at first glance:
files = dir_a.glob("*")
(equal, _, _) = filecmp.cmpfiles(dir_a, dir_b, files, shallow=False)
print("equal:", *equal)
However, in the full example below, you will see that this code fails to detect
that two files are actually different.
"""Demo behavior of filecmp.cmpfiles with absolute path names."""
import filecmp
import tempfile
from pathlib import Path
with tempfile.TemporaryDirectory() as tmpdirname:
# prepare two different files
tmpdir = Path(tmpdirname)
dir_a = tmpdir / "a"
dir_b = tmpdir / "b"
file_a = dir_a / "foo.txt"
file_b = dir_b / "foo.txt"
dir_a.mkdir()
dir_b.mkdir()
file_a.write_text("A")
file_b.write_text("B")
# actually diff the files
files = dir_a.glob("*")
# filecmp should issue a warning here!
(equal, _, _) = filecmp.cmpfiles(dir_a, dir_b, files, shallow=False)
# otherwise, this result is easy to misinterpret - files are reported as
equal
print("equal:", *equal)
----------
components: Library (Lib)
messages: 411570
nosy: bers
priority: normal
severity: normal
status: open
title: Explicit or correct behavior of filecmp.cmpfiles w/ absolute path names
type: behavior
versions: Python 3.9
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Python tracker <[email protected]>
<https://bugs.python.org/issue46512>
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