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gh-84538: add strict argument to pathlib.PurePath.relative_to (GH-19813)

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By default, :meth:`pathlib.PurePath.relative_to` doesn't deal with paths that are not a direct prefix of the other, raising an exception in that instance. This change adds a *walk_up* parameter that can be set to allow for using ``..`` to calculate the relative path.

example:
```
>>> p = PurePosixPath('/etc/passwd')
>>> p.relative_to('/etc')
PurePosixPath('passwd')
>>> p.relative_to('/usr')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "pathlib.py", line 940, in relative_to
    raise ValueError(error_message.format(str(self), str(formatted)))
ValueError: '/etc/passwd' does not start with '/usr'
>>> p.relative_to('/usr', strict=False)
PurePosixPath('../etc/passwd')
```


https://bugs.python.org/issue40358

Automerge-Triggered-By: GH:brettcannon
This commit is contained in:
domragusa 2022-10-29 01:20:14 +02:00 • committed by GitHub
parent 72fa57a8fe
commit e089f23bbb
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6 changed files with 150 additions and 21 deletions
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48
Lib/pathlib.py
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@ -626,10 +626,13 @@ class PurePath(object):
return self._from_parsed_parts(self._drv, self._root,
self._parts[:-1] + [name])
def relative_to(self, *other):
def relative_to(self, *other, walk_up=False):
"""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.
The *walk_up* parameter controls whether `..` may be used to resolve
the path.
"""
# For the purpose of this method, drive and root are considered
# separate parts, i.e.:
@ -644,20 +647,35 @@ class PurePath(object):
abs_parts = [drv, root] + parts[1:]
else:
abs_parts = parts
to_drv, to_root, to_parts = self._parse_args(other)
if to_root:
to_abs_parts = [to_drv, to_root] + to_parts[1:]
other_drv, other_root, other_parts = self._parse_args(other)
if other_root:
other_abs_parts = [other_drv, other_root] + other_parts[1:]
else:
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):
formatted = self._format_parsed_parts(to_drv, to_root, to_parts)
raise ValueError("{!r} is not in the subpath of {!r}"
" OR one path is relative and the other is absolute."
.format(str(self), str(formatted)))
return self._from_parsed_parts('', root if n == 1 else '',
abs_parts[n:])
other_abs_parts = other_parts
num_parts = len(other_abs_parts)
casefold = self._flavour.casefold_parts
num_common_parts = 0
for part, other_part in zip(casefold(abs_parts), casefold(other_abs_parts)):
if part != other_part:
break
num_common_parts += 1
if walk_up:
failure = root != other_root
if drv or other_drv:
failure = casefold([drv]) != casefold([other_drv]) or (failure and num_parts > 1)
error_message = "{!r} is not on the same drive as {!r}"
up_parts = (num_parts-num_common_parts)*['..']
else:
failure = (root or drv) if num_parts == 0 else num_common_parts != num_parts
error_message = "{!r} is not in the subpath of {!r}"
up_parts = []
error_message += " OR one path is relative and the other is absolute."
if failure:
formatted = self._format_parsed_parts(other_drv, other_root, other_parts)
raise ValueError(error_message.format(str(self), str(formatted)))
path_parts = up_parts + abs_parts[num_common_parts:]
new_root = root if num_common_parts == 1 else ''
return self._from_parsed_parts('', new_root, path_parts)
def is_relative_to(self, *other):
"""Return True if the path is relative to another path or False.