How Can I Find Overlapping Matches Using Python's `re.findall()`?

Understanding Overlapping Matches in Regex

By default, the findall() method in Python's re module doesn't capture overlapping matches within a string. This behavior can be confusing, especially when matches consist of consecutive characters.

Consider the following code:

match = re.findall(r'\w\w', 'hello')
print(match)

Output:

['he', 'll']

This pattern matches two consecutive word characters (w). As expected, he and ll are returned. However, el and lo are not captured, despite appearing in the string.

Overcoming Overlapping Matches

To capture overlapping matches, we can use a lookahead assertion (?=...). This assertion matches a specific pattern but doesn't consume any characters from the string. Instead, it checks if the following characters match the assertion.

For example:

match1 = re.findall(r'(?=(\w\w))', 'hello')
print(match1)

Output:

['he', 'el', 'll', 'lo']

In this case, (?=(ww)) matches any location where two consecutive word characters exist without actually consuming them. This allows findall() to return both overlapping and non-overlapping matches.

Explanation

The regex /(?=(ww)) can be broken down as follows:

• (?:...) is a non-capturing group, which means the contents of the group are not returned.
• ww matches two consecutive word characters.
• (?=...) is the lookahead assertion, which ensures that the string contains ww at the current location but does not consume them.

By using this approach, we can effectively detect all overlapping matches within a string, even when they consist of consecutive characters.

The above is the detailed content of How Can I Find Overlapping Matches Using Python's `re.findall()`?. For more information, please follow other related articles on the PHP Chinese website!