[issue37130] pathlib.with_name() doesn't like unnamed files.

[N.P. Khelili]

New submission from N.P. Khelili <nophke at free.fr>:

Hi guys!

I'm new to python and working on my first real project with it....
I'm sorry if it's not the right place for posting this.

I noticed that that pathlib.with_name() method does not accept to give a name to a path that does not already have one.

It seems a bit inconsistent knowing that the Path constructor does not require one...

>>> Path()
PosixPath('.')

>>> Path().resolve()
PosixPath('/home/nono')

but:
 
>>> Path().with_name('dodo')

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.7/pathlib.py", line 819, in with_name
    raise ValueError("%r has an empty name" % (self,))
ValueError: PosixPath('.') has an empty name

whereas if you do:

>>> Path().resolve().with_name('dodo')
PosixPath('/home/dodo')

I first tought "explicit is better than implicit" and then why not allways use resolve first! That was not a big deal but then I tried:

>>> Path('..').with_name('dudu').resolve()
PosixPath('/home/nono/dudu')

( ! )

>>> Path('..').resolve().with_name('dudu')
PosixPath('/dudu')

It seems that the dots and slashes are in fact not really interpreted leading to:

>>> Path('../..').with_name('dudu')
PosixPath('../dudu')

>>> Path('../..').with_name('dudu').resolve()
PosixPath('/home/dudu')

( ! )
 
>>> Path('../..').resolve().with_name('dudu')

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.7/pathlib.py", line 819, in with_name
    raise ValueError("%r has an empty name" % (self,))
ValueError: PosixPath('/') has an empty name

Even if the doc briefly tells about this, I found this behavior quite disturbing....

I don't know what could be the correct answer to this,
maybe making Path('..') as invalid as Path('.'),
or adding a few more lines in the doc...

Sincerly yours,

----------
components: Library (Lib)
messages: 344250
nosy: Nophke
priority: normal
severity: normal
status: open
title: pathlib.with_name() doesn't like unnamed files.
type: behavior
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37130>
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