Splitting Strings in Python with Separator variable

Question

I'm trying to write a function to split a string with given separators. I've seen answers to similar questions that have use regular expressions to ignore all special characters, but I want to be able to pass in a variable of separators.

So far I've got:

def split_string(source, separators): 
    source_list = source
    for separator in separators:
        if separator in source_list:
                source_list.replace(separator, ' ') 
    return source_list.split()

But it's not removing the separators

.split takes a regular expression in python; why can't you use source.split(separators)? What is separators exactly? (like an example) — Explosion Pills
– Explosion Pills, Commented Feb 6, 2013 at 3:21
@ExplosionPills str.split() doesn't take a regex, it just takes a string - (if you want a regex, that's re.split()). — Gareth Latty
– Gareth Latty, Commented Feb 6, 2013 at 3:21
@ExplosionPills -- I hope you mean .replace takes a selection of characters... — mgilson
– mgilson, Commented Feb 6, 2013 at 3:23

mgilson · Accepted Answer · 2013-02-06 04:36:53Z

5

The regex solution (to me) seems like it would be pretty easy:

import re
def split_string(source,separators):
    return re.split('[{0}]'.format(re.escape(separators)),source)

example:

>>> import re
>>> def split_string(source,separators):
...     return re.split('[{0}]'.format(re.escape(separators)),source)
... 
>>> split_string("the;foo: went to the store",':;')
['the', 'foo', ' went to the store']

The reason for using a regex here is in the event that you don't want to have ' ' in your separators, this will still work ...

An alternative (which I think I prefer), where you could have multi-character separators is:

def split_string(source,separators):
    return re.split('|'.join(re.escape(x) for x in separators),source)

In this case, the multi-character separators things get passed in as some sort of non-string iterable (e.g. a tuple or a list), but single character separators can still be passed in as a single string.

>>> def split_string(source,separators):
...     return re.split('|'.join(re.escape(x) for x in separators),source)
... 
>>> split_string("the;foo: went to the store",':;')
['the', 'foo', ' went to the store']
>>> split_string("the;foo: went to the store",['foo','st'])
['the;', ': went to the ', 'ore']

Or, finally, if you want to split on consecutive runs of separators as well:

def split_string(source,separators):
    return re.split('(?:'+'|'.join(re.escape(x) for x in separators)+')+',source)

which gives:

>>> split_string("Before the rain ... there was lightning and thunder.", " .")
['Before', 'the', 'rain', 'there', 'was', 'lightning', 'and', 'thunder', '']

edited Feb 6, 2013 at 4:36

answered Feb 6, 2013 at 3:25

mgilson

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4 Comments

bsiddiqui Over a year ago

I tried this: out = split_string("Before the rain ... there was lightning and thunder.", " .") print out and got this back: ['Before', '', 'the', 'rain', '', '', '', '', '', '', '', 'there', 'was', 'lightning', 'and', 'thunder', '']

mgilson Over a year ago

@BasilSiddiqui -- That's looks like what I would expect. What did you expect?

bsiddiqui Over a year ago

I was expecting ['Before', 'the', 'rain', 'there', 'was', 'lightning', 'and', 'thunder']

mgilson Over a year ago

@BasilSiddiqui -- See my final edit. It gets you really close using the same basic formalism.

steveha · Accepted Answer · 2013-02-06 03:28:25Z

2

The problem is that source_list.replace(separator, ' ') does not modify source_list in place; it just returns a modified string value. But you don't do anything with this modified value, so it is lost.

You can do this:

source_list = source_list.replace(separator, ' ')

Then source_list will now have the modified version. I made this one change to your function and then it worked perfectly when I tested it.

edited Feb 6, 2013 at 3:28

answered Feb 6, 2013 at 3:23

steveha

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Comments

Guddu · Accepted Answer · 2013-02-06 03:28:59Z

2

You forgot to assign the result of source_list.replace(separator, ' ') back to source_list

Look at this modified snippet

def split_string(source, separators): 
    source_list = source
    for separator in separators:
        if separator in source_list:
                source_list=source_list.replace(separator, ' ') 
    return source_list.split()

answered Feb 6, 2013 at 3:28

Guddu

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Comments

Mahdi Yusuf · Accepted Answer · 2013-02-06 03:23:31Z

0

you should be using split to solve the issue, it doesn't take regex but you can make it work to do what you need.

In your example code you dont reassign.

answered Feb 6, 2013 at 3:23

Mahdi Yusuf

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