[issue35787] shlex.split inserts extra item on backslash space space

[Eric V. Smith]

Eric V. Smith  added the comment:

I agree that the current behavior makes sense. I think "preserve the literal 
value of the next character" means the space won't be interpreted as a 
separator.

In the first example (I think better written as shlex.split(r'a \ b')), the 
first space is a separator. The second space is not a separator because of the 
backslash, so it's part of the second token ' b'.

In the second example (shlex.split(r'a \  b')), the first space is a separator, 
the second space is not a separator because of the backslash, and the third 
space is a separator. This explains why there's no space before the 'b'.

I assume peter.otten's example is bash. I can confirm with zsh:

[~]$ python3 -c 'import sys; print(sys.argv)' a   b
['-c', 'a', 'b']
[~]$ python3 -c 'import sys; print(sys.argv)' a \ b
['-c', 'a', ' b']
[~]$ python3 -c 'import sys; print(sys.argv)' a \  b
['-c', 'a', ' ', 'b']

I'm going to close this. But anyone wants to suggest a documentation patch, 
feel free to reopen this.

Also, changing this would no doubt break some code, so I'd recommend against 
changing it even if I didn't think it was doing the right thing.

--
nosy: +eric.smith
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed
type:  -> behavior

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[issue35787] shlex.split inserts extra item on backslash space space

[Peter Otten]

Peter Otten <__pete...@web.de> added the comment:

To me the current shlex behaviour makes sense, and the shell (tested with bash) 
behaves the same way:

$ python3 -c 'import sys; print(sys.argv)' a   b
['-c', 'a', 'b']
$ python3 -c 'import sys; print(sys.argv)' a \  b
['-c', 'a', ' ', 'b']

--
nosy: +peter.otten

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[issue35787] shlex.split inserts extra item on backslash space space

[Max]

New submission from Max :

I believe in both cases below, the ouptu should be ['a', 'b']; the extra ' ' 
inserted in the list is incorrect:

python3.6
Python 3.6.2 (default, Aug  4 2017, 14:35:04)
[GCC 6.3.0 20170516] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import shlex
>>> shlex.split('a \ b')
['a', ' b']
>>> shlex.split('a \  b')
['a', ' ', 'b']
>>>

Doc reference: https://docs.python.org/3/library/shlex.html#parsing-rules
> Non-quoted escape characters (e.g. '\') preserve the literal value of the 
> next character that follows;

I believe this implies that backslash space should be just space; and then two 
adjacent spaces should be used (just like a single space) as a separator 
between arguments.

--
components: Library (Lib)
messages: 334081
nosy: max
priority: normal
severity: normal
status: open
title: shlex.split inserts extra item on backslash space space
versions: Python 3.6

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