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Improve pathname2url() and url2pathname() docs (#127125)
These functions have long sown confusion among Python developers. The existing documentation says they deal with URL path components, but that doesn't fit the evidence on Windows: >>> pathname2url(r'C:\foo') '///C:/foo' >>> pathname2url(r'\\server\share') '////server/share' # or '//server/share' as of quite recently If these were URL path components, they would imply complete URLs like `file://///C:/foo` and `file://////server/share`. Clearly this isn't right. Yet the implementation in `nturl2path` is deliberate, and the `url2pathname()` function correctly inverts it. On non-Windows platforms, the behaviour until quite recently is to simply quote/unquote the path without adding or removing any leading slashes. This behaviour is compatible with *both* interpretations -- 1) the value is a URL path component (existing docs), and 2) the value is everything following `file:` (this commit) The conclusion I draw is that these functions operate on everything after the `file:` prefix, which may include an authority section. This is the only explanation that fits both the Windows and non-Windows behaviour. It's also a better match for the function names.
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Doc/library/urllib.request.rst

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@@ -148,9 +148,15 @@ The :mod:`urllib.request` module defines the following functions:
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.. function:: pathname2url(path)
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Convert the pathname *path* from the local syntax for a path to the form used in
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the path component of a URL. This does not produce a complete URL. The return
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value will already be quoted using the :func:`~urllib.parse.quote` function.
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Convert the given local path to a ``file:`` URL. This function uses
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:func:`~urllib.parse.quote` function to encode the path. For historical
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reasons, the return value omits the ``file:`` scheme prefix. This example
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shows the function being used on Windows::
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>>> from urllib.request import pathname2url
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>>> path = 'C:\\Program Files'
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>>> 'file:' + pathname2url(path)
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'file:///C:/Program%20Files'
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.. versionchanged:: 3.14
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Windows drive letters are no longer converted to uppercase.
@@ -161,11 +167,17 @@ The :mod:`urllib.request` module defines the following functions:
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found in any position other than the second character.
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.. function:: url2pathname(path)
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.. function:: url2pathname(url)
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Convert the given ``file:`` URL to a local path. This function uses
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:func:`~urllib.parse.unquote` to decode the URL. For historical reasons,
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the given value *must* omit the ``file:`` scheme prefix. This example shows
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the function being used on Windows::
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Convert the path component *path* from a percent-encoded URL to the local syntax for a
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path. This does not accept a complete URL. This function uses
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:func:`~urllib.parse.unquote` to decode *path*.
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>>> from urllib.request import url2pathname
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>>> url = 'file:///C:/Program%20Files'
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>>> url2pathname(url.removeprefix('file:'))
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'C:\\Program Files'
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.. versionchanged:: 3.14
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Windows drive letters are no longer converted to uppercase.

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