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bpo-40358: add strict parameter to pathlib.PurePath.relative_to #19807

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bpo-40358: add strict parameter to pathlib.PurePath.relative_to #19807

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b3daa47
add tests for pathlib.PurePath.relative_to(strict=False)
domragusa Apr 29, 2020
9892f8b
add strict option for pathlib.PurePath.relative_to
domragusa Apr 29, 2020
3c10a8c
documentation for PurePath.relative_to strict parameter
domragusa Apr 30, 2020
f1fb0a2
add missing news entry
domragusa Apr 30, 2020
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add strict option for pathlib.PurePath.relative_to
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@domragusa
domragusa committed Apr 29, 2020
commit 9892f8bfe5e5dd44f47fc37770ae28275ddd85f3
28 changes: 21 additions & 7 deletions Lib/pathlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -895,10 +895,10 @@ def with_suffix(self, suffix):
return self._from_parsed_parts(self._drv, self._root,
self._parts[:-1] + [name])

def relative_to(self, *other):
def relative_to(self, *other, strict=True):
"""Return the relative path to another path identified by the passed
arguments. If the operation is not possible (because this is not
a subpath of the other path), raise ValueError.
related to the other path), raise ValueError.
"""
# For the purpose of this method, drive and root are considered
# separate parts, i.e.:
Expand All @@ -920,12 +920,26 @@ def relative_to(self, *other):
to_abs_parts = to_parts
n = len(to_abs_parts)
cf = self._flavour.casefold_parts
if (root or drv) if n == 0 else cf(abs_parts[:n]) != cf(to_abs_parts):
common = 0
for p, tp in zip(cf(abs_parts), cf(to_abs_parts)):
if p != tp:
break
common += 1
if strict:
failure = (root or drv) if n == 0 else common != n
error_message = "{!r} does not start with {!r}"
up_parts = []
else:
failure = root != to_root
if drv or to_drv:
failure = cf([drv]) != cf([to_drv]) or (failure and n > 1)
error_message = "{!r} is not related to {!r}"
up_parts = (n-common)*['..']
if failure:
formatted = self._format_parsed_parts(to_drv, to_root, to_parts)
raise ValueError("{!r} does not start with {!r}"
.format(str(self), str(formatted)))
return self._from_parsed_parts('', root if n == 1 else '',
abs_parts[n:])
raise ValueError(error_message.format(str(self), str(formatted)))
return self._from_parsed_parts('', root if common == 1 else '',
up_parts+abs_parts[common:])

def is_relative_to(self, *other):
"""Return True if the path is relative to another path or False.
Expand Down