[issue33968] os.makedirs and empty string

[Emily Morehouse]

Change by Emily Morehouse :


--
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue33968] os.makedirs and empty string

[Emily Morehouse]

Emily Morehouse  added the comment:

The os.path conventions do follow, '' and '.' are not treated the same here 
either --

>>> os.path.exists('')
False
>>> os.path.exists('.')
True
>>> os.path.isdir('')
False
>>> os.path.isdir('.')
True

The only os.path function that I see as potentially confusing in this 
discussion is dirname, as that can return an empty string which yields 
unexpected results when used as an argument for other functions.

>>> os.path.dirname('testdir')
''
>>> os.path.dirname('./testdir')
'.'

However, changing this functionality (e.g. os.path.dirname('testdir') returning 
'.') would result in backward-compatibility issues that would not be warranted 
(IMO).


I'll leave the final word to Serhiy to close out as 'not a bug' at his 
discretion.

--
assignee:  -> emilyemorehouse
nosy: +serhiy.storchaka

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[issue33968] os.makedirs and empty string

[Carl Andersson]

Carl Andersson  added the comment:

That is in essence what I am looking for, yes.

As you say, it's not pretty. My opinion is still that if the os.path convention 
is that '' is the same as '.', this should be respected.

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[issue33968] os.makedirs and empty string

[Emily Morehouse]

Emily Morehouse  added the comment:

I'll defer to Serhiy's os.path expertise, but from what I know -- os.dirname is 
essentially a helper function for returning the first item of split. 

What I'm gathering is that you're looking for a more advanced way of parsing a 
file path -- say "nested/dir/sample.txt" -- to "nested/dir" while also handling 
parsing "" into ".". 

Not the prettiest, but you could wrap os.path.dirname in os.path.normpath:

>>> os.path.normpath(os.path.dirname("nested/dir/sample.txt"))
'nested/dir'
>>> os.path.normpath(os.path.dirname(""))
'.'

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[issue33968] os.makedirs and empty string

[Carl Andersson]

Carl Andersson  added the comment:

I can see the point in keeping the behaviour close to the OS-level commands, 
but the discrepancy between os.mkdir (or os.makedirs) and os.path.dirname is 
not resolved.

I still think that
>>> os.makedirs(os.path.dirname(filename), exist_ok=True)
should be able to handle the case when "filename" does not contain any 
directories.
A possible workaround would be to use os.path.abspath somewhere in the mix.

In my humble opinion creating the directory structure required to write a file 
should not require this level of complexity, since it is such a common 
operation.

--
nosy:  -serhiy.storchaka

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[issue33968] os.makedirs and empty string

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Concur with Emily.

--
nosy: +serhiy.storchaka

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[issue33968] os.makedirs and empty string

[Emily Morehouse]

Emily Morehouse  added the comment:

This is an interesting behavior to note. I think the current behavior makes the 
most sense, as it corresponds to the OS-level errors that you get from running 
the same operations.

Interestingly, at least on Unix-based file systems, we get different error 
messages but the same behavior when using "" vs "." as our target:

[linux]$ mkdir ""
mkdir: cannot create directory ‘’: No such file or directory
[linux]$ mkdir .
mkdir: cannot create directory ‘.’: File exists

[mac]$ mkdir ""
mkdir: .: No such file or directory
[mac]$ mkdir .
mkdir: .: File exists

Both os.mkdir and os.makedirs follow (only os.mkdir is included as the 
traceback is cleaner, but they raise the same errors):
>>> os.mkdir("")
Traceback (most recent call last):
  File "", line 1, in 
FileNotFoundError: [Errno 2] No such file or directory: ''
>>> os.mkdir(".")
Traceback (most recent call last):
  File "", line 1, in 
FileExistsError: [Errno 17] File exists: '.'


Since on an OS level the only time "File exists" is returned is when using "." 
and not "", os.makedirs with exists_ok=True also follows:

>>> os.makedirs("", exist_ok=True)
Traceback (most recent call last):
  File "", line 1, in 
  File 
"/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/os.py",
 line 220, in makedirs
mkdir(name, mode)
FileNotFoundError: [Errno 2] No such file or directory: ''
>>> os.makedirs(".", exist_ok=True)
>>>

Basically, the FileExistsError gets silenced, but FileNotFoundError is left 
alone. I can see how the differences are nuanced and not obvious though.


Unless you think there is a succinct and worthwhile way of adding this to the 
documentation, I think this issue can be closed.

--
nosy: +emilyemorehouse

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[issue33968] os.makedirs and empty string

[Carl Andersson]

New submission from Carl Andersson :

os.makedirs does not handle the empty string the same way as the os.path.XX 
functions does. This is (to me) unexpected behaviour, since calls like 
`os.makedirs(os.path.dirname(filename), exist_ok=True)` raises an exception if 
`filename` does not contain any directories.
Also, it raises an `FileNotFoundError` regardless of the `exist_ok` flag. I 
would expect `os.makedirs('')` to fail with `FileExistsError` and 
`os.makedirs('', exist_ok=True)` to not do anything.

--
components: Library (Lib)
messages: 320486
nosy: CarlAndersson
priority: normal
severity: normal
status: open
title: os.makedirs and empty string
type: behavior
versions: Python 3.6

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