Can Python Regex Capture Repeated Subpatterns Effectively?

Capturing Repeated Subpatterns in Python Regex

When matching complex patterns, capturing repeating subpatterns can enhance regex performance. While Python regular expressions have limitations in repeating captures, there are workarounds to effectively capture desired patterns.

Splitting and Concatenation

One approach, suggested in the provided answer, is to match the entire pattern initially and split the subpatterns later. This approach simplifies the regex but requires additional steps for splitting. For instance, consider matching email addresses:

import re

pattern = r'(.+?)@(\w+\.\w+)'
text = "yasar@webmail.something.edu.tr"

match = re.match(pattern, text)
if match:
    email_address, domain = match.groups()
    subdomains = domain.split(".")

Regex Groups

If the pattern is more complex and the subpatterns have distinct characteristics, regex groups (i.e., parentheses) can be used to capture them directly. Consider the following pattern:

pattern = r'(\w+)?\((\d+) entries?\)'

This pattern matches a word and an optional parenthetical expression containing a number and the text "entries" (or "entry"). The captured groups are accessible through the match object:

text = "Received 10 entries for yesterday"

match = re.match(pattern, text)
if match:
    word, count = match.groups()
    if word:
        print("Word:", word)
    if count:
        print("Count:", count)

This approach allows for direct capture of subpatterns without the need for complex splitting routines.

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