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240 CHAPTER 10 ■ BATTERIES INCLUDED
The function re.split splits a string by the occurrences of a pattern. This is similar to the
string method split, except that you allow full regular expressions instead of only a fixed separator
string. For example, with the string method split you could split a string by the occurrences
of the string ', ' but with re.split you can split on any sequence of space characters and commas:
>>> some_text = 'alpha, beta,,,,gamma delta'
>>> re.split('[, ]+', some_text)
['alpha', 'beta', 'gamma', 'delta']
■Note If the pattern contains parentheses, the parenthesized groups are interspersed between the
split substrings.
As you can see from this example, the return value is a list of substrings. The maxsplit
argument indicates the maximum number of splits allowed:
>>> re.split('[, ]+', some_text, maxsplit=2)
['alpha', 'beta', 'gamma delta']
>>> re.split('[, ]+', some_text, maxsplit=1)
['alpha', 'beta,,,,gamma delta']
The function re.findall returns a list of all occurrences of the given pattern. For example,
to find all words in a string, you could do the following:
>>> pat = '[a-zA-Z]+'
>>> text = '"Hm... Err -- are you sure?" he said, sounding insecure.'
>>> re.findall(pat, text)
['Hm', 'Err', 'are', 'you', 'sure', 'he', 'said', 'sounding', 'insecure']
Or, you could find the punctuation:
>>> pat = r'[.?\-",]+'
>>> re.findall(pat, text)
['"', '...', '--', '?"', ',', '.']
Note that the dash (-) has been escaped so Python won’t interpret it as part of a character
range (such as a–z).
The function re.sub is used to substitute the leftmost, nonoverlapping occurrences of a
pattern with a given replacement. Consider the following example:
>>> pat = '{name}'
>>> text = 'Dear {name}...'
>>> re.sub(pat, 'Mr. Gumby', text)
'Dear Mr. Gumby...'
See the section “Using Group Numbers and Functions in Substitutions” later in this chapter
for information on how to use this function more effectively.