Python split string with space unless a \ is in front

Question

Sorry if this post is a bit confusing to read this is my first post on this site and this is a hard question to ask, I have tried my best. I have also tried googling and i can not find anything.

I am trying to make my own command line like application in python and i would like to know how to split a string if a "\" is not in front of a space and to delete the backslash.

This is what i mean.

>>> c = "play song I\ Want\ To\ Break\ Free"
>>> print c.split(" ")
['play', 'song', 'I\\', 'Want\\', 'To\\', 'Break\\', 'Free']

When I split c with a space it keeps the backslash however it removes the space. This is how I want it to be like:

>>> c = "play song I\ Want\ To\ Break\ Free"
>>> print c.split(" ")
['play', 'song', 'I ', 'Want ', 'To ', 'Break ', 'Free']

If someone can help me that would be great!

Also if it needs Regular expressions could you please explain it more because I have never used them before.

Edit: Now this has been solved i forgot to ask is there a way on how to detect if the backslash has been escaped or not too?

I misread at first; you do want to split on spaces, but when a space is preceded by a backslash, you want to preserve the space as part of the split string. check. — Martijn Pieters
– Martijn Pieters, Commented Apr 18, 2014 at 17:46

nneonneo · Accepted Answer · 2014-04-18 18:23:03Z

14

It looks like you're writing a commandline parser. If that's the case, may I recommend shlex.split? It properly splits a command string according to shell lexing rules, and handles escapes properly. Example:

>>> import shlex
>>> shlex.split('play song I\ Want\ To\ Break\ Free')
['play', 'song', 'I Want To Break Free']

answered Apr 18, 2014 at 18:23

nneonneo

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3 Comments

iProgram Over a year ago

BINGO! Exactly what I want! It even knows not to split if it's in quotes! Thanks. :) This is useful because it's going to be an input from raw_input() so if it has quotes then don't split! Thanks.

Martijn Pieters Over a year ago

@aPyDeveloper: And I thought that you wanted to produce the demonstrated output! :-)

iProgram Over a year ago

It has got the output I want

Martijn Pieters · Accepted Answer · 2014-04-18 18:13:18Z

2

Just split on the space, then replace any string ending with a backslash with with one ending in a space instead:

[s[:-1] + ' ' if s.endswith('\\') else s for s in c.split(' ')]

This is a list comprehension; c is split on spaces, and each resulting string is examined for a trailing \ backslash at the end; if so, the last character is removed and a space is added.

One slight disadvantage: if the original string ends with a backslash (no space), that last backslash is also replaced by a space.

Demo:

>>> c = r"play song I\ Want\ To\ Break\ Free"
>>> [s[:-1] + ' ' if s.endswith('\\') else s for s in c.split(' ')]
['play', 'song', 'I ', 'Want ', 'To ', 'Break ', 'Free']

To handle escaped backslashes, you'd count the number of backslashes. An even number means the backslash is escaped:

[s[:-1] + ' ' if s.endswith('\\') and (len(s) - len(s.rstrip('\\'))) % 2 == 1 else s
 for s in c.split(' ')]

Demo:

>>> c = r"play song I\ Want\ To\ Break\\ Free"
>>> [s[:-1] + ' ' if s.endswith('\\') and (len(s) - len(s.rstrip('\\'))) % 2 == 1 else s
...  for s in c.split(' ')]
['play', 'song', 'I ', 'Want ', 'To ', 'Break\\\\', 'Free']

edited Apr 18, 2014 at 18:13

answered Apr 18, 2014 at 17:41

Martijn Pieters

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4 Comments

Rose Kunkel Over a year ago

What does this do if the string ends in a backslash?

Martijn Pieters Over a year ago

@WilliamKunkel: the last backslash is also replaced. Hrmz.

iProgram Over a year ago

I have also just updated my questurn if you would like to help me on it too! ;)

Martijn Pieters Over a year ago

@aPyDeveloper: You'd have to count the number of backslashes at the end of the string; if it is even then the backslash was escaped. len(s) - len(s.rstrip('\\')) would tell you how many backslashes there are at the end of the string.

s3c · Accepted Answer · 2025-06-04 07:08:15Z

0

Here's a noob one-liner no one has explored yet, that doesn't require any libraries. Note that you may use anything that is not already in the string instead of {{PlaceholderSpace}}:

s = 'play song I\ Want\ To\ Break\ Free'  
s = s.replace("\ ", "{{PlaceholderSpace}}")  # 'play song I{{PlaceholderSpace}}Want{{PlaceholderSpace}}To{{PlaceholderSpace}}Break{{PlaceholderSpace}}Free'  
l = s.split()  # ['play', 'song', 'I{{PlaceholderSpace}}Want{{PlaceholderSpace}}To{{PlaceholderSpace}}Break{{PlaceholderSpace}}Free']  
s = [e.replace("{{PlaceholderSpace}}", " ") for e in l]  # ['play', 'song', 'I Want To Break Free']  
  
# or in one-liner  
  
s = [e.replace("{{PlaceholderSpace}}", " ") for e in s.replace("\ ", "{{PlaceholderSpace}}").split()]

answered Jun 4 at 7:08

s3c

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1 Comment

s3c Jun 4 at 9:06

I tend to use just {{}}

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