bpo-23082: Better error message for PurePath.relative_to() from pathlib (GH-19611)
Co-authored-by: Sadhana Srinivasan <rotuna@Sadhanas-MBP.fritz.box>
(cherry picked from commit 448325369ff73011d34d6c3a493014fe3ead8843)
Co-authored-by: Rotuna <sadhanasrinivasan@protonmail.com>
diff --git a/Doc/library/pathlib.rst b/Doc/library/pathlib.rst
index 83f7c83..bf6fee4 100644
--- a/Doc/library/pathlib.rst
+++ b/Doc/library/pathlib.rst
@@ -551,7 +551,9 @@
File "<stdin>", line 1, in <module>
File "pathlib.py", line 694, in relative_to
.format(str(self), str(formatted)))
- ValueError: '/etc/passwd' does not start with '/usr'
+ ValueError: '/etc/passwd' is not in the subpath of '/usr' OR one path is relative and the other absolute.
+
+ NOTE: This function is part of :class:`PurePath` and works with strings. It does not check or access the underlying file structure.
.. method:: PurePath.with_name(name)
diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index f98d69e..9f5e27b 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -922,7 +922,8 @@
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} does not start with {!r}"
+ 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:])
diff --git a/Misc/NEWS.d/next/Library/2020-04-20-22-08-36.bpo-23082.iX90Id.rst b/Misc/NEWS.d/next/Library/2020-04-20-22-08-36.bpo-23082.iX90Id.rst
new file mode 100644
index 0000000..13ed0de
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-04-20-22-08-36.bpo-23082.iX90Id.rst
@@ -0,0 +1 @@
+Updated the error message and docs of PurePath.relative_to() to better reflect the function behaviour.
\ No newline at end of file