How to use Python regular expressions for performance optimization-Python Tutorial-php.cn

How to use Python regular expressions for performance optimization

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Release： 2023-06-23 11:39:19

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Python is a very commonly used programming language, often used for tasks such as data processing and analysis. In Python, regular expressions are a very important tool that can be used to extract required information from text. Because Python's regular expressions are very powerful, if you don't pay attention to performance optimization when using them, it will cause problems such as slow program running and long time consumption. This article will introduce how to use Python regular expressions for performance optimization to improve the efficiency of regular expression processing.

Use native strings

Strings in Python can be represented by single quotes or double quotes, but if there are special symbols in the string, they need to be escaped. This results in slow regular expression processing. In order to solve this problem, you can use raw string notation, that is, add "r" in front of the string, so that special symbols do not need to be escaped.

For example:

text = r"hello,world
"

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Be careful when using "."

The "." in regular expressions is usually used to match any character. However, if you directly use "." to match, it will have a great impact on performance. This is because "." will match any character except newlines, and if there are many newlines in the text, the matching speed will slow down.

To avoid this problem, we can use non-greedy mode to match any character that is not a newline character. The non-greedy mode method is to add "?" after ".", so that only the first newline character is matched, and not all the way to the end of the file.

For example:

text = "hello
world"
# 匹配出hello
re.findall(r".*?", text)

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Avoid using capture groups

In regular expressions, brackets "()" are used to group, but if you use capture Capturing group, that is, writing an expression within parentheses, can be used in subsequent matching. However, capturing groups can cause performance degradation because information about the expression within the parentheses needs to be recorded during matching.

In order to avoid this problem, you can use a non-capturing group, that is, add "?:" before the brackets, so that it will not affect performance.

For example:

text = "hello,world"
# 使用捕获组
re.findall(r"(hello)", text)
# 使用非捕获组
re.findall(r"(?:hello)", text)

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Use precompilation

When you need to use the same regular expression multiple times, precompilation can greatly improve the regular expression s efficiency. Precompilation can parse the syntax of a regular expression once and use it until the program exits, thus avoiding the performance loss of parsing each time.

For example:

pattern = re.compile(r"hello")
text = "hello,world"
# 预编译
pattern.findall(text)

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Avoid using greedy mode

Greedy mode (greedy mode) refers to matching as many characters as possible. If greedy mode is used in regular expressions, the matching range will be too large, thus affecting performance. This problem can be avoided by using non-greedy mode.

For example:

text = "<html>hello,world</html>"
# 使用贪婪模式
re.findall(r"<.*>", text)
# 使用非贪婪模式
re.findall(r"<.*?>", text)

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Summary: The above are the performance optimization methods of Python regular expressions, including using native strings, avoiding the use of ".", avoiding the use of capturing groups, using precompilation and avoiding Use greedy mode etc. If the above methods can be used correctly, the efficiency of regular expression processing can be greatly improved, making data processing and analysis in Python more efficient.

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