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?

Answer 1

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']

Answer 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']