urllib.request.pathname2url() mishandles UNC paths

[barneygale]

Bug report

Bug description:

When given a Windows UNC path, urllib.request.pathname2url() incorrectly generates a URI that begins with four slashes. The correct number is two, see ref1, ref2.

>>> import urllib.request
>>> urllib.request.pathname2url(r'\\server\share')
'////server/share'

Furthermore, when given an extended UNC path like \\?\unc\server\share, pathname2url() incorrectly generates a URI that begins with only one slash:

>>> urllib.request.pathname2url(r'\\?\unc\server\share')
'/server/share'

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• GH-126205: Fix conversion of UNC paths to file URIs #126208
• [3.12] GH-126205: Fix conversion of UNC paths to file URIs (GH-126208) #126248
• [3.13] GH-126205: Fix conversion of UNC paths to file URIs (GH-126208) #126249