Regular Expressions
Regular expressions (regex) are powerful tools for pattern matching and text manipulation. They are implemented using the re module . Here's a basic rundown:
Import the module: First, you need to import the re module.
Python Code
import re
Creating a regular expression pattern: Regular expressions are written as strings with a special syntax to define patterns you want to search for.
Python Code
pattern = r"pattern"
The r before the string indicates a raw string literal, which is used to ignore escape characters.
Matching patterns: can use re.search() to search for the pattern within a string. This method returns a match object if the pattern is found, otherwise, it returns None.
Python Code
match = re.search(pattern, text)
if match:
print("Pattern found:", match.group())
else:
print("Pattern not found")
Basic Patterns:
Literal Characters: Ordinary characters match themselves. For example, the pattern r"cat" matches the string "cat".
Character Classes: can use character classes to match specific types of characters. For example, \d matches any digit, \w matches any alphanumeric character, \s matches any whitespace character.
Quantifiers: Quantifiers specify the number of occurrences of a character or group. For example, + matches one or more occurrences, * matches zero or more occurrences, matches zero or one occurrence, {n} matches exactly n occurrences.
Anchors: Anchors are used to specify the position in the string where the match should occur. For example, ^ matches the start of a string, $ matches the end of a string.
Groups and Capture: can use parentheses to create groups and capture parts of the matched string.
Example:
Python Code
import re
text = "The cat sat on the mat."
pattern = r"cat"
match = re.search(pattern, text)
if match:
print("Pattern found:", match.group())
else:
print("Pattern not found")
This will output:
Pattern found: cat
Regular expressions can get quite complex, but they're incredibly useful once you get the hang of them. Just be careful not to overcomplicate things when simpler methods would suffice.