In Python, how do I split a string and keep the separators?

Question

Here\'s the simplest way to explain this. Here\'s what I\'m using:

re.split(\'\\W\', \'foo/bar spam\\neggs\')
-> [\'foo\', \'bar\', \'spam\', \'eggs\']
         


        

Answer 1

I found this generator based approach more satisfying:

def split_keep(string, sep):
    """Usage:
    >>> list(split_keep("a.b.c.d", "."))
    ['a.', 'b.', 'c.', 'd']
    """
    start = 0
    while True:
        end = string.find(sep, start) + 1
        if end == 0:
            break
        yield string[start:end]
        start = end
    yield string[start:]

It avoids the need to figure out the correct regex, while in theory should be fairly cheap. It doesn't create new string objects and, delegates most of the iteration work to the efficient find method.

... and in Python 3.8 it can be as short as:

def split_keep(string, sep):
    start = 0
    while (end := string.find(sep, start) + 1) > 0:
        yield string[start:end]
        start = end
    yield string[start:]