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Regex

Regular Expressions

Regular expressions are a sequence of characters that define a search pattern. They are used to match, locate, and manipulate text. In Python, regular expressions are implemented using the re module.

Here are some examples of regular expressions:

  • r"hello\s+world": Matches the string "hello world" with any number of spaces between "hello" and "world".
  • r"\d+": Matches one or more digits.
  • r"\w+": Matches one or more word characters (letters, digits, and underscores).
  • r"[\w\s]+": Matches one or more word characters or spaces.
  • r"[\w\s]+@[\w\s]+\.[\w]{2,3}": Matches an email address with a username, domain name, and top-level domain.

Using Regular Expressions in Python

  1. Import the re module:
import re
  1. Use the re.search() function to search for a pattern in a string:
string = "The quick brown fox jumps over the lazy dog"
pattern = r"fox"
match = re.search(pattern, string)
if match:
    print("Match found:", match.group())
else:
    print("Match not found")
  1. Use the re.findall() function to find all occurrences of a pattern in a string:
string = "The quick brown fox jumps over the lazy dog"
pattern = r"\b\w{3}\b"
matches = re.findall(pattern, string)
print("Matches:", matches)
  1. Use the re.sub() function to replace all occurrences of a pattern in a string with a new string:
string = "The quick brown fox jumps over the lazy dog"
pattern = r"fox"
new_string = re.sub(pattern, "cat", string)
print("New string:", new_string)

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