[New-bugs-announce] [issue42958] filecmp.cmp(shallow=True) isn't actually shallow when only mtime differs

[Alexander Vandenbulcke]

New submission from Alexander Vandenbulcke <alexander.vandenbulcke95 at gmail.com>:

Consider the case where 2 files are shallow compared where only the mtime differs (i.e. the mode and size is identical).

With filecmp.cmp(f1, f2, shallow=True) a deep compare would be performed behind the scenes since the guard clauses fell through. This discrepancy is either a problem in the docstring or a problem in the comparison itself.

Two options remain:
- the documentation is altered and describes that, in case only the mtime differs (i.e. mode and size are equal) a deep compare is performed
- the behaviour is restricted in that effectively only a shallow compare is performed
- a shallow compare becomes more restrictive (do not consider the mtime during the compare)

My preference is to adjust the function to safeguard the meaning of 'shallow' in this context.

----------
components: Library (Lib)
messages: 385225
nosy: AlexVndnblcke
priority: normal
severity: normal
status: open
title: filecmp.cmp(shallow=True) isn't actually shallow when only mtime differs
type: behavior

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42958>
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