Effective way to iteratively append to a string in Python?

Question

I'm writing a Python function to split text into words, ignoring specified punctuation. Here is some working code. I'm not convinced that constructing strings out of lists (buf = [] in the code) is efficient though. Does anyone have a suggestion for a better way to do this?

def getwords(text, splitchars=' \t|!?.;:"'):
    """
    Generator to get words in text by splitting text along specified splitchars
    and stripping out the splitchars::

      >>> list(getwords('this is some text.'))
      ['this', 'is', 'some', 'text']
      >>> list(getwords('and/or'))
      ['and', 'or']
      >>> list(getwords('one||two'))
      ['one', 'two']
      >>> list(getwords(u'hola unicode!'))
      [u'hola', u'unicode']
    """
    splitchars = set(splitchars)
    buf = []
    for char in text:
        if char not in splitchars:
            buf.append(char)
        else:
            if buf:
                yield ''.join(buf)
                buf = []
    # All done. Yield last word.
    if buf:
        yield ''.join(buf)

Answer 1

You don't want to use re.split?

import re
re.split("[,; ]+", "coucou1 ,   coucou2;coucou3")

Answer 2

http://www.skymind.com/~ocrow/python_string/ talks about several ways of concatenating strings in Python and assesses their performance as well.

Answer 3

You can split the input using re.split():

>>> splitchars=' \t|!?.;:"'
>>> re.split("[%s]" % splitchars, "one\ttwo|three?four")
['one', 'two', 'three', 'four']
>>>

EDIT: If your splitchars may contain special chars like ] or ^, you can use re.escpae()

>>> re.escape(splitchars)
'\\ \\\t\\|\\!\\?\\.\\;\\:\\"'
>>> re.split("[%s]" % re.escape(splitchars), "one\ttwo|three?four")
['one', 'two', 'three', 'four']
>>>

Answer 4

You can use re.split

re.split('[\s|!\?\.;:"]', text)

However if the text is very large the resulting array may be consuming too much memory. Then you may consider re.finditer:

import re
def getwords(text, splitchars=' \t|!?.;:"'):
  words_iter = re.finditer(
    "([%s]+)" % "".join([("^" + c) for c in splitchars]),
    text)
  for word in words_iter:
    yield word.group()

# a quick test
s = "a:b cc? def...a||"
words = [x for x in getwords(s)]
assert ["a", "b", "cc", "def", "a"] == words, words