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Python Regular Expressions (RegEx) Basic Matching

In Python, the re module allows you to work with regular expressions to search, match, and manipulate strings. Regular expressions are patterns used to match character sequences in text.

Importing the re Module

import re
  

Basic Matching Using re.match()

import re

pattern = r"Hello"
text = "Hello, World!"

# Check if the pattern matches at the beginning
match = re.match(pattern, text)
if match:
    print("Match found:", match.group())
else:
    print("No match")
# Output: Match found: Hello
  

Explanation:

• re.match(pattern, text): Checks for a match only at the beginning of the string.
• match.group(): Returns the matched text.

Searching Anywhere in the String Using re.search()

pattern = r"World"
text = "Hello, World!"

search = re.search(pattern, text)
if search:
    print("Found:", search.group())
# Output: Found: World
  

Explanation:

• re.search(): Searches for the pattern anywhere in the string, not just at the beginning.

Finding All Matches Using re.findall()

text = "Python 3.9, Python 3.10, Python 3.11"
pattern = r"Python \d+\.\d+"

matches = re.findall(pattern, text)
print(matches)
# Output: ['Python 3.9', 'Python 3.10', 'Python 3.11']
  

Explanation:

• re.findall() returns a list of all matches in the string.
• \d+ matches one or more digits, \. matches a literal dot.

Key Points

• Use re.match() for matching at the start of a string.
• Use re.search() to find a pattern anywhere in the string.
• Use re.findall() to get all occurrences of a pattern.
• Regular expressions allow complex string matching, extraction, and validation.

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Python regular expressions are powerful tools for pattern matching, text extraction, and string validation, making data parsing and manipulation efficient.