pathlib.Path.relative_to 对比 os.path.relpath

Question

我想找到两个绝对路径之间的相对路径。我现有的代码通常使用 pathlib.Path 与文件系统交互，但我运行遇到了一个问题，这个问题似乎很容易用 os.path.relpath 解决，但（到目前为止）用 pathlib.Path.

我有：

(A)，目录的绝对路径，/home/project/cluster-scope/base/namespaces/acm
(B)，相对路径从(A)到另一个目录，../../../components/monitoring-rbac
(C)，第二个目录的绝对路径，/home/project/cluster-scope/base/core/namespaces/acm

我想计算从 (C) 到 (B) 的新相对路径。这有效：

>>> import os
>>> path_A = '/home/project/cluster-scope/base/namespaces/acm'
>>> path_B = '../../../components/monitoring-rbac'
>>> path_C = '/home/project/cluster-scope/base/core/namespaces/acm'
>>> path_B_abs = os.path.abspath(os.path.join(path_A, path_B))
>>> os.path.relpath(path_B_abs, path_C)
'../../../../components/monitoring-rbac'

但这不是：

>>> from pathlib import Path
>>> path_A = Path('/home/project/cluster-scope/base/namespaces/acm')
>>> path_B = Path('../../../components/monitoring-rbac')
>>> path_C = Path('/home/project/cluster-scope/base/core/namespaces/acm')
>>> path_B_abs = (path_A / path_B).resolve()
>>> path_B_abs.relative_to(path_C)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.9/pathlib.py", line 928, in relative_to
    raise ValueError("{!r} is not in the subpath of {!r}"
ValueError: '/home/project/cluster-scope/components/monitoring-rbac' is not in the subpath of '/home/project/cluster-scope/base/core/namespaces/acm' OR one path is relative and the other is absolute.

ValueError 异常中的消息似乎不准确，或者在最少误导：这两条路径显然共享一个共同的父路径。是有什么方法可以使用 pathlib.Path？我意识到我可以只使用 os.path.relpath 并完成它，但我很好奇我是否误解了 pathlib 的 relative_to 方法的使用。

Answer 1

显然这是不可能的。根据an issue:

I agree it's worth improving the error message (and probably the docs too).

It's never made clear that relative_to only looks deeper (won't ever generate leading ".." parts) - the closest hint in the docs is that os.path.relpath is different (and that isn't even in the relative_to() section).

在当前版本中 docstring 说

"""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.
"""

pathlib.Path.relative_to 对比 os.path.relpath

pathlib.Path.relative_to vs os.path.relpath

python

filesystems

pathlib