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[951] Understanding the pattern of "(.*?)" in Python's re package

发布时间 2023-11-22 13:16:48作者: McDelfino

In Python's regular expressions, (.*?) is a capturing group with a non-greedy quantifier. 

Let's break down the components:

  1. ( and ): Parentheses are used to create a capturing group. This allows us to capture a portion of the matched text.
  2. .*?: Inside the capturing group, .*? is a non-greedy quantifier that matches any character (except for a newline) zero or more times. The * means "zero or more occurrences", and the ? makes the * non-greedy, meaning it will match as few characters as possible while still allowing the overall pattern to match.
    So, (.*?) is capturing any sequence of characters (including an empty sequence) but doing so in a non-greedy way. This is useful when we want to capture the shortest possible substring that allows the overall pattern to match.

Here is a brief example to illustrate the difference between greedy and non-greedy quantifiers:

import re

text = "abc123def456ghi"

# Greedy match
greedy_match = re.search(r'(.*)\d', text)
if greedy_match:
    print("Greedy match:", greedy_match.group(1))  # Output: abc123def45

# Non-greedy match
non_greedy_match = re.search(r'(.*?)\d', text)
if non_greedy_match:
    print("Non-greedy match:", non_greedy_match.group(1))  # Output: abc

In the greedy match, (.*)\d captures as much as possible before the last digit, while in the non-greedy match, (.*?)\d captures as little as possible before the first digit. The non-greedy approach is often useful when you want to extract the shortest substring between two specific patterns.