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Adjust path_to_url et al. to produce the same results on Python 3.14+ #13423

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Jul 25, 2025
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Adjust path_to_url et al. to produce the same results on Python 3.14+ #13423

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1 change: 1 addition & 0 deletions news/13423.bugfix.rst
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Fix remaining test failures in Python 3.14 by adjusting ``path_to_url`` and similar functions.
7 changes: 6 additions & 1 deletion src/pip/_internal/models/link.py
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Expand Up @@ -6,6 +6,7 @@
import os
import posixpath
import re
import sys
import urllib.parse
from collections.abc import Mapping
from dataclasses import dataclass
Expand Down Expand Up @@ -131,7 +132,11 @@ def _clean_file_url_path(part: str) -> str:
# should not be quoted. On Linux where drive letters do not
# exist, the colon should be quoted. We rely on urllib.request
# to do the right thing here.
return urllib.request.pathname2url(urllib.request.url2pathname(part))
ret = urllib.request.pathname2url(urllib.request.url2pathname(part))
if sys.version_info >= (3, 14):
# https://discuss.python.org/t/pathname2url-changes-in-python-3-14-breaking-pip-tests/97091
ret = ret.removeprefix("//")
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I am not proud of this :(

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It wasn't obvious to me how else to do this either 🙁

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Is there something in cpython we can reference here so people reading this later knows what’s going on?

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I can try digging a reference to the change.

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Ideally, if we could find something that explained why cpython changed what they did, and why the new result is "correct" and why pip needs something different from the "correct" answer, that would be best (as it would give us a much better basis for informed decisions if this code ever needs to change again).

Unfortunately, I get the impression that there's no real "correct" answer here, and the cpython change was "because it's more consistent with (something or other that pip maybe doesn't even care about)". If so, then documenting what precisely pip is using to base its idea of what "the url for a pathname" is, would be better than nothing.

Worst case scenario would be that there's simply no standard for how to convert a pathname to a URL in general, and it's all just a mess of guesswork and hacks 🙁

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What form should the input to url2pathname take? It seems like it should take a file: URL with the initial file: removed.

I'll list the URLs with file: prefixes so it's a little easier to grok:

  • file:foo - relative path
  • file:///foo - absolute path (POSIX), path beginning with single slash (Windows)
  • file:///c:/foo - DOS drive path (Windows)
  • file://server/foo - UNC path (Windows)

But that's only part of the story - does it accept all the various variants of file: URLs (things like file:/etc/hosts, and the various ways of encoding Windows drives)?

In 3.14 it should do, yeah. Acceptable slash-prefix variants:

  • file:/foo - absolute path (POSIX), path beginning with single slash (Windows)
  • file:c:/foo, file:/c:/foo - DOS drive path (Windows)
  • file:////server/foo, file://///server/foo - UNC path (Windows)

Windows DOS paths also support a pipe (|) rather than a colon after the drive letter.

The authority can also vary for non-UNC paths.

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@barneygale barneygale Jul 19, 2025 •
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Is the "correct" form accepted in all Python versions, or was there an actual bug in <=3.13 which mean that we can't just pass correct forms and be done with it? If the latter is the case, what was the bug in 3.13? Because converting correct form to "acceptable-to-3.13" form seems like a better fix than hacking up the output.

It should be accepted in the latest versions of 3.12 and 3.13 (see list of backported changes), but in older versions they're mishandled.

Is pathname2url always correct, or were there bugs in that in 3.13? If so, did those bugs take the form of returning an incorrect URL? If so, what's incorrect about the output, because we'd need to know that to "fix up" the return value.

The major 3.14-only change here is that pathname2url('/tmp') now returns '///tmp', whereas in 3.13 it returns '/tmp'. Otherwise it's a similar story to url2pathname above - the latest bugfix releases of 3.13 and 3.12 are fine, but older maintenance releases (and anything before 3.12) is buggy

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As a very basic example, I cannot see why url2pathname(pathname2url(path)) shouldn't be the identity (or at worst, normalise the path). I can understand that pathname2url(url2pathname(url)) might be a little more complicated, as there are many ways to encode a path (certainly on Windows) as a URL, so what you get back might be different to what you passed. But even then, I'd expect it to the original URL and the returned one to represent the same path.

Can you share examples of where this isn't the case? Paths should roundtrip

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Can you share examples of where this isn't the case? Paths should roundtrip

Sorry, I'm getting confused. The pip code is

ret = urllib.request.pathname2url(urllib.request.url2pathname(part))

which I misread as path -> URL -> path. So I couldn't see why that wasn't (effectively) a null operation. But it's not, it's the other way around, making it (in effect) a URL normalisation operation.

If that's the case, my understanding of what's going on has definitely been helped by this discussion, because I couldn't have said that before1. But I'm now left with another question, which is why, if we're returning a normalised URL (with the file: prefix omitted), we even care about the extra 2 slashes. I feel like we're either doing some incorrect parsing on the returned URL, or we're (incorrectly) treating it as a path rather than a schemeless URL somewhere 🙁

Or, to put this another way, I think that removing the // is simply patching over a more significant bug in our handling of the return value from this function, and we should be looking for that bug, rather than trying to undo the changes CPython made.

Of course, there's also a "practicality beats purity" question here - if this means pip doesn't work on Python 3.14, we might need to make the expedient choice in order to get a fix into pip 25.2, which is the release that will end up in Python 3.14, and will be the current release when 3.14 is released.

Footnotes

  1. We should definitely include a comment above that code saying that it's normalising the provided URL. ↩

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But I'm now left with another question, which is why, if we're returning a normalised URL (with the file: prefix omitted), we even care about the extra 2 slashes.

I think our motivating care is that the tests no longer pass. Pip is not apparently broken on the Python 3.14 betas.

So it's a question of modifying the function to keep the behavior consistent across Python versions, or modifying the tests, and the later requires significantly more confidence about what the right behavior is.

return ret


# percent-encoded: /
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2 changes: 1 addition & 1 deletion src/pip/_internal/utils/urls.py
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Expand Up @@ -12,7 +12,7 @@ def path_to_url(path: str) -> str:
quoted path parts.
"""
path = os.path.normpath(os.path.abspath(path))
url = urllib.parse.urljoin("file:", urllib.request.pathname2url(path))
url = urllib.parse.urljoin("file://", urllib.request.pathname2url(path))
return url


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2 changes: 1 addition & 1 deletion tests/unit/test_urls.py
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Expand Up @@ -11,7 +11,7 @@
def test_path_to_url_unix() -> None:
assert path_to_url("/tmp/file") == "file:///tmp/file"
path = os.path.join(os.getcwd(), "file")
assert path_to_url("file") == "file://" + urllib.request.pathname2url(path)
assert path_to_url("file") == "file://" + path


@pytest.mark.skipif("sys.platform != 'win32'")
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