What functions do regular expressions have?

Regular expressions include match(), search(), findall(), sub(), split(), compile() and other functions. Detailed description: 1. match(), used to check whether a string matches a specified pattern; 2. search(), used to search for a specified pattern in a string; 3. findall(), used to search in a string Search for all matching substrings in the string and return them in list form; 4. sub(), used to search for a specified pattern in a string, etc.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

Regular expression is a tool used to describe string patterns, which can help us find, replace and match operations in text. In regular expressions, there are many functions that can be used to implement different functions. Let's introduce some commonly used regular expression functions in detail.

match()

The match() function is used to check whether a string matches a specified pattern. Returns the matched string if the match is successful, or None if the match fails. For example, we can use the match() function to check if a string starts with a specified prefix.

import re
pattern = r'hello'
string = 'hello world'
result = re.match(pattern, string)
if result:
    print('匹配成功')
else:
    print('匹配失败')

search()

The search() function is used to search for a specified pattern in a string. It starts searching from the beginning of the string and returns immediately once a matching substring is found, without continuing to search backwards. For example, we can use the search() function to search whether a string contains a specified substring.

import re
pattern = r'world'
string = 'hello world'
result = re.search(pattern, string)
if result:
    print('匹配成功')
else:
    print('匹配失败')

findall()

findall() function is used to search for all matching substrings in a string and return them in the form of a list. For example, we can use the findall() function to find all numbers in a string.

import re
pattern = r'\d+'
string = '123abc456def789ghi'
result = re.findall(pattern, string)
print(result)  # 输出：['123', '456', '789']

sub()

sub() function is used to search for a specified pattern in a string and replace the matching substring with the specified string . For example, we can use the sub() function to replace all numbers in a string with specified characters.

import re
pattern = r'\d+'
string = '123abc456def789ghi'
result = re.sub(pattern, 'X', string)
print(result)  # 输出：XabcXdefXghi

split()

split() function is used to split a string into several substrings according to the specified pattern and return it in the form of a list. For example, we can use the split() function to split a string into substrings based on commas.

import re
pattern = r','
string = 'apple,banana,orange'
result = re.split(pattern, string)
print(result)  # 输出：['apple', 'banana', 'orange']

compile()

compile() function is used to compile a regular expression string pattern into a regular expression object, thereby improving matching efficiency. The compiled regular expression object can be used repeatedly, avoiding the need to recompile the pattern string each time. For example, we can use the compile() function to compile a regular expression string pattern into a regular expression object.

import re
pattern = r'\d+'
regex = re.compile(pattern)
string = '123abc456def789ghi'
result = regex.findall(string)
print(result)  # 输出：['123',456', '789']

The above are some commonly used regular expression functions. Through these functions, we can easily perform search, replacement and matching operations in text to achieve our needs for string patterns. Of course, regular expressions have more functions and functions, which require us to continuously learn and master them in practical applications.

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