How to find overlapping matches with a regexp?
overlapping, python, regex
Solution
`findall` doesn't yield overlapping matches by default. This expression does however:
>>> re.findall(r'(?=(\w\w))', 'hello')
['he', 'el', 'll', 'lo']
Here `(?=...)` is a lookahead assertion:
`(?=...)` matches if `...` matches next, but doesn’t consume any of the string. This is called a lookahead assertion. For example, `Isaac (?=Asimov)` will match `'Isaac '` only if it’s followed by `'Asimov'`.
Problem
``` >>> match = re.findall(r'\w\w', 'hello') >>> print match ['he', 'll'] ``` Since \w\w means two characters, 'he' and 'll' are expected. But why do 'el' and 'lo' not match the regex? ``` >>> match1 = re.findall(r'el', 'hello') >>> print match1 ['el'] >>> ```