[issue44316] Support preserving path meaning in os.path.normpath() and abspath()

[Eryk Sun]

Eryk Sun  added the comment:

I think separate keep_curdir and keep_pardir options is over-complicating the 
signature. Also, I'd prefer to remove a dot component if it's not the first 
component since there's no reason to keep it.

If you plan to use normpath() in pathlib, then the case for special_prefixes in 
ntpath.normpath() should be removed. Actually, it never should have been added. 
IIRC it was added as a workaround for a buggy implementation that's no longer 
an issue. Only \\?\ is special, and that's only when opening/accessing a path. 
It's not special in GetFullPathNameW(), as is called by ntpath.abspath() in 
Windows. This needlessly introduces inconsistency for ntpath.abspath() calls in 
Windows vs Unix.

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[issue44316] Support preserving path meaning in os.path.normpath() and abspath()

[Barney Gale]

Barney Gale  added the comment:

I think I agree

How would you feel about two new arguments? Following `os.curdir` and 
`os.pardir` names:

def normpath(path, *, keep_curdir=False, keep_pardir=False)
...

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[issue44316] Support preserving path meaning in os.path.normpath() and abspath()

[Eryk Sun]

Eryk Sun  added the comment:

> single dots are collapsed

For pathlib, I've previously discussed a desire to retain a leading dot 
component from the initializing path. This could be implemented in strict mode 
for normpath(). 

A leading dot is significant in the path of an executable in a search context, 
such as the first item in the args sequence of subprocess.Popen(). For example, 
if "./spam" is normalized as "spam", then the system will search the PATH 
directories instead of the current working directory. It's also import to note 
that in Windows a leading dot component is required in order to preclude 
searching even if the path contains slashes. For example, CreateProcessW() and 
SearchPathW() will try to resolve r"spam\eggs.exe" against every directory in 
the search path, whereas r".\spam\eggs.exe" is explicitly relative to just the 
current working directory.

Retaining a leading dot component can also be important in Windows in order to 
disambiguate a drive-relative path from a named data stream of a file that has 
a single-letter filename. For example, "C:spam" is a file named "spam" in the 
working path on drive "C:" (e.g. "C:spam" -> r"C:\working\path\spam"), but 
r".\C:spam" is a data stream named "spam" in a file named "C" in the current 
working directory.

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nosy: +eryksun

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[issue44316] Support preserving path meaning in os.path.normpath() and abspath()

[Barney Gale]

Barney Gale  added the comment:

For this bug specifically, the pathlib docs describe the desirable behaviour:



Spurious slashes and single dots are collapsed, but double dots ('..') are not, 
since this would change the meaning of a path in the face of symbolic links:

>>> PurePath('foo//bar')
PurePosixPath('foo/bar')
>>> PurePath('foo/./bar')
PurePosixPath('foo/bar')
>>> PurePath('foo/../bar')
PurePosixPath('foo/../bar')

(a naïve approach would make PurePosixPath('foo/../bar') equivalent to 
PurePosixPath('bar'), which is wrong if foo is a symbolic link to another 
directory)



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[issue44316] Support preserving path meaning in os.path.normpath() and abspath()

[Barney Gale]

Barney Gale  added the comment:

Thanks Terry, I've added a topic here: 
https://discuss.python.org/t/pathlib-and-os-path-code-duplication-and-feature-parity/9239

The bit about `normpath()` is towards the middle of the post.

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[issue44316] Support preserving path meaning in os.path.normpath() and abspath()

[Barney Gale]

Change by Barney Gale :


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keywords: +patch
pull_requests: +25279
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/26694

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[issue44316] Support preserving path meaning in os.path.normpath() and abspath()

[Terry J. Reedy]

Terry J. Reedy  added the comment:

I think you should propose this for discussion on python-ideas list to try for 
more support. If you can, say more about why reconsider.

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nosy: +terry.reedy
versions: +Python 3.11

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[issue44316] Support preserving path meaning in os.path.normpath() and abspath()

[Barney Gale]

New submission from Barney Gale :

>>> os.path.normpath('a/./b/../c//.')
'a/c'
>>> pathlib.Path('a/./b/../c//.')
PosixPath('a/b/../c')

pathlib takes care not to change the meaning of the path when normalising. That 
means preserving '..' entries, as these can't be simplified without resolving 
symlinks etc.

normpath(), on the other handle, /always/ eliminates '..' entries, which can 
change the meaning of the path.

We could add a new argument to `normpath()` and `abspath()` that leaves '..' 
entries intact. This was closed as "won't fix" back in bpo-2289, but I think 
it's worth re-considering.

This enhancement would be helpful for my longer-term work to make pathlib an 
OOP wrapper of os + os.path, rather than a parallel implementation.

--
components: Library (Lib)
messages: 395122
nosy: barneygale
priority: normal
severity: normal
status: open
title: Support preserving path meaning in os.path.normpath() and abspath()
type: enhancement

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