How do I split a string into a list of words?

Use str.split():

Return a list of the words in the string, using sep as the delimiter ... If sep is not specified or is None, a different splitting algorithm is applied: runs of consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace.

>>> line = "a sentence with a few words"
>>> line.split()
['a', 'sentence', 'with', 'a', 'few', 'words']

Depending on what you plan to do with your sentence-as-a-list, you may want to look at the Natural Language Took Kit. It deals heavily with text processing and evaluation. You can also use it to solve your problem:

import nltk
words = nltk.word_tokenize(raw_sentence)

This has the added benefit of splitting out punctuation.

Example:

>>> import nltk
>>> s = "The fox's foot grazed the sleeping dog, waking it."
>>> words = nltk.word_tokenize(s)
>>> words
['The', 'fox', "'s", 'foot', 'grazed', 'the', 'sleeping', 'dog', ',', 
'waking', 'it', '.']

This allows you to filter out any punctuation you don't want and use only words.

Please note that the other solutions using string.split() are better if you don't plan on doing any complex manipulation of the sentence.

[Edited]