Regex Metacharacters
Regex Character Sets
These notes cover Python’s regular expression character sets. Character sets allow you to match one character from a specified group.
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Basic Syntax: Character sets are defined using square brackets
1. For example,[abc]]matches ‘a’, ‘b’, or ‘c’. -
Ranges: You can specify ranges of characters using a hyphen.
[a-z]]matches any lowercase letter,[0-9]]matches any digit, and[A-Z]]matches any uppercase letter. You can combine ranges:[a-zA-Z0-9]]matches any alphanumeric character. -
Negation: A caret
^at the beginning of a character set negates it.[^abc]]matches any character except ‘a’, ‘b’, or ‘c’.[^0-9]]matches any non-digit character. -
Special Characters: Inside character sets, most Regex Metacharacters lose their special meaning except for
\(backslash),^(caret - when at the beginning), and-(hyphen). To match a literal]](closing square bracket), place it first or escape it with a backslash\]]. To match a literal-, place it at the beginning or end, or escape it with\-. To match a literal^, place it anywhere other than the beginning, or escape it. -
Examples:
import re
string = "Hello, World! 123"
# Match any lowercase vowel
match = re.findall(r"[aeiou]]", string) # Output: ['e', 'o', 'o']]
# Match any digit
match = re.findall(r"[0-9]]", string) # Output: ['1', '2', '3']]
# Match any character except a space
match = re.findall(r"[^ ]]", string) #Output: ['H', 'e', 'l', 'l', 'o', ',', 'W', 'o', 'r', 'l', 'd', '!', '1', '2', '3']]
# Match any uppercase or lowercase letter
match = re.findall(r"[a-zA-Z]]", string) # Output: ['H', 'e', 'l', 'l', 'o', 'W', 'o', 'r', 'l', 'd']]
# Matching a literal ]]
match = re.findall(r"1abc]]", "abc1") #Output: ['abc]]']]
#Matching a literal -
match = re.findall(r"[-abc]]", "abc-def") #Output: ['-']]
#Matching a literal ^
match = re.findall(r"[^abc]]", "abc^def") #Output: ['^']]