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Tutorials > Python > Regular Expressions

Regular Expressions

Regular expressions are a powerful tool for pattern matching and manipulation of text data. In Python, the re module provides support for regular expressions.

A regular expression is a sequence of characters that defines a search pattern. In Python, regular expressions are defined as strings, and you can use special characters and metacharacters in the pattern to match different types of characters or groups of characters.

Here are some of the most common metacharacters used in regular expressions:

  • . (dot): Matches any single character except a newline character.
  • * (asterisk): Matches zero or more occurrences of the preceding character or group.
  • + (plus): Matches one or more occurrences of the preceding character or group.
  • ? (question mark): Matches zero or one occurrence of the preceding character or group.
  • {m,n}: Matches between m and n occurrences of the preceding character or group.
  • [] (brackets): Matches any character specified inside the brackets.
  • [^] (negated brackets): Matches any character not specified inside the brackets.
  • ^ (caret): Matches the start of a string.
  • $ (dollar sign): Matches the end of a string.

Here's an example of using regular expressions in Python:

python
Copy code
import re

text = "The quick brown fox jumps over the lazy dog."

# Find all occurrences of the word "the" in the text
result = re.findall(r"the", text)
print(result) # Output: ['the', 'the']

# Replace all occurrences of the word "the" with "a"
result = re.sub(r"the", "a", text)
print(result) # Output: 'a quick brown fox jumps over a lazy dog.'

# Check if the text starts with the word "The"
result = re.match(r"^The", text)
print(result) # Output: <re.Match object; span=(0, 3), match='The'>

In this example, the re.findall function is used to find all occurrences of the word "the" in the text. The re.sub function is used to replace all occurrences of the word "the" with "a". The re.match function is used to check if the text starts with the word "The".

Regular expressions can be a bit tricky to master, but they are very useful for many text processing tasks, such as validating inputs, parsing text data, and searching and manipulating text.



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