How can i parse a comma delimited string into a list (caveat)?

Question

I need to be able to take a string like:

'''foo, bar, "one, two", three four'''

into:

['foo', 'bar', 'one, two', 'three four']

I have an feeling (with hints from #python) that the solution is going to involve the shlex module.

Answer 1

It depends how complicated you want to get... do you want to allow more than one type of quoting. How about escaped quotes?

Your syntax looks very much like the common CSV file format, which is supported by the Python standard library:

import csv
reader = csv.reader(['''foo, bar, "one, two", three four'''], skipinitialspace=True)
for r in reader:
  print r

Outputs:

['foo', 'bar', 'one, two', 'three four']

HTH!

Answer 2

The shlex module solution allows escaped quotes, one quote escape another, and all fancy stuff shell supports.

>>> import shlex
>>> my_splitter = shlex.shlex('''foo, bar, "one, two", three four''', posix=True)
>>> my_splitter.whitespace += ','
>>> my_splitter.whitespace_split = True
>>> print list(my_splitter)
['foo', 'bar', 'one, two', 'three', 'four']

escaped quotes example:

>>> my_splitter = shlex.shlex('''"test, a",'foo,bar",baz',bar \xc3\xa4 baz''',
                              posix=True) 
>>> my_splitter.whitespace = ',' ; my_splitter.whitespace_split = True 
>>> print list(my_splitter)
['test, a', 'foo,bar",baz', 'bar \xc3\xa4 baz']

Answer 3

You may also want to consider the csv module. I haven't tried it, but it looks like your input data is closer to CSV than to shell syntax (which is what shlex parses).

Answer 4

You could do something like this:

>>> import re
>>> pattern = re.compile(r'\s*("[^"]*"|.*?)\s*,')
>>> def split(line):
...  return [x[1:-1] if x[:1] == x[-1:] == '"' else x
...          for x in pattern.findall(line.rstrip(',') + ',')]
... 
>>> split("foo, bar, baz")
['foo', 'bar', 'baz']
>>> split('foo, bar, baz, "blub blah"')
['foo', 'bar', 'baz', 'blub blah']

Answer 5

I'd say a regular expression would be what you're looking for here, though I'm not terribly familiar with Python's Regex engine.

Assuming you use lazy matches, you can get a set of matches on a string which you can put into your array.

Answer 6

If it doesn't need to be pretty, this might get you on your way:

def f(s, splitifeven):
    if splitifeven & 1:
        return [s]
    return [x.strip() for x in s.split(",") if x.strip() != '']

ss = 'foo, bar, "one, two", three four'

print sum([f(s, sie) for sie, s in enumerate(ss.split('"'))], [])