Master Python Regex: Greedy vs Non‑Greedy Patterns Explained
This article walks through the difference between greedy and non‑greedy regular expression patterns in Python, shows practical code examples, visual output, and even demonstrates how to use named groups for more precise matching.
Introduction
Hello, I’m PiPi. Recently a fan asked a question about Python regular expressions, specifically the greedy and non‑greedy modes, which sparked a lively discussion. I’m sharing the details here for everyone to learn.
Solution Process
Below is a solution provided by the expert Xiao Wang, including a sample code snippet.
import re
txt = "This is an HTML tag: <head>HEADER</head>. It means the head of the whole HTML document."
pattern1 = re.compile(r"<.*>")
pattern2 = re.compile(r"<.*?>")
result1 = re.findall(pattern1, txt)
result2 = re.findall(pattern2, txt)
print(result1)
print(result2)The output is shown in the following image:
Explanation: The goal is to match the data inside HTML tags, i.e., the content between < and >. The two patterns differ only by a trailing ?, but the effect is significant.
The greedy pattern matches as much as possible, while the non‑greedy pattern stops at the first closing bracket.
Bonus: Named Groups
Here is an alternative using named groups for clearer matching.
import re
txt = "This is an HTML tag: <head>HEADER</head>. It means the head of the whole HTML document."
tag = re.compile(r"<(?P<tag_mark>[A-Za-z0-9]+)>.*?</(?P=tag_mark)>.*")
print(re.findall(tag, txt))Conclusion
This article, based on a fan’s question, explains the greedy and non‑greedy modes of Python regular expressions, provides code demonstrations, and shows how to use named groups for more precise matches.
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