List of Basic Regular Expression Patterns in Python

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Complete List of Basic Regular Expression Patterns in Python

Character Classes

PatternDescriptionExample
[abc]Matches any one of the characters a, b, or c[aeiou] matches any vowel
[^abc]Matches any character except a, b, or c[^0-9] matches non-digits
[a-z]Matches any character in range a to z[a-z] matches lowercase letters
[A-Z]Matches any character in range A to Z[A-Z] matches uppercase letters
[0-9]Matches any digit[0-9] matches digits 0-9
[a-zA-Z]Matches any letter[a-zA-Z] matches all letters
[a-zA-Z0-9_]Equivalent to \wMatches word characters

Predefined Character Classes

PatternDescriptionEquivalent
.Matches any character except newline
\dMatches any digit[0-9]
\DMatches any non-digit[^0-9]
\wMatches any word character[a-zA-Z0-9_]
\WMatches any non-word character[^a-zA-Z0-9_]
\sMatches any whitespace character[ \t\n\r\f\v]
\SMatches any non-whitespace character[^ \t\n\r\f\v]

Anchors (Position Matchers)

PatternDescriptionExample
^Matches start of string (or line with re.MULTILINE)^Hello matches “Hello” at start
$Matches end of string (or line with re.MULTILINE)world$ matches “world” at end
\bMatches word boundary\bword\b matches “word” as whole word
\BMatches non-word boundary\Bword\B matches “word” inside other words

Quantifiers (Repetition)

PatternDescriptionExample
*0 or more occurrencesa* matches “”, “a”, “aa”, “aaa”, …
+1 or more occurrencesa+ matches “a”, “aa”, “aaa”, …
?0 or 1 occurrencea? matches “” or “a”
{n}Exactly n occurrencesa{3} matches “aaa”
{n,}n or more occurrencesa{2,} matches “aa”, “aaa”, “aaaa”, …
{n,m}Between n and m occurrencesa{2,4} matches “aa”, “aaa”, “aaaa”

Alternation and Grouping

PatternDescriptionExample
``OR operator (alternation)`catdog` matches “cat” or “dog”
()Grouping and capturing(abc)+ matches “abc”, “abcabc”, etc.
(?:)Non-capturing group(?:abc)+ groups without capturing

Escape Sequences

PatternDescriptionExample
\\Backslash\\ matches “”
\.Literal dot\. matches “.”
\*Literal asterisk\* matches “*”
\+Literal plus\+ matches “+”
\?Literal question mark\? matches “?”
\(Literal opening parenthesis\( matches “(“
\)Literal closing parenthesis\) matches “)”
\[Literal opening bracket\[ matches “[“
\]Literal closing bracket\] matches “]”
\{Literal opening brace\{ matches “{“
\}Literal closing brace\} matches “}”
\^Literal caret\^ matches “^”
\$Literal dollar\$ matches “$”
|Literal pipe| matches ““

Special Sequences

PatternDescriptionExample
\AMatches only at start of string\AStart
\ZMatches only at end of stringend\Z
\nNewline character
\tTab character
\rCarriage return
\fForm feed
\vVertical tab

Practical Examples with Each Pattern Type

python

import re

# Character Classes
text = "abc123XYZ"
print(re.findall(r'[a-z]', text))        # ['a', 'b', 'c']
print(re.findall(r'[^0-9]', text))       # ['a', 'b', 'c', 'X', 'Y', 'Z']

# Predefined Classes
text = "Hello 123 World!"
print(re.findall(r'\d', text))           # ['1', '2', '3']
print(re.findall(r'\w', text))           # ['H', 'e', 'l', 'l', 'o', '1', '2', '3', 'W', 'o', 'r', 'l', 'd']

# Anchors
text = "Hello world\nHello python"
print(re.findall(r'^Hello', text))       # ['Hello'] (start of string)
print(re.findall(r'^Hello', text, re.MULTILINE))  # ['Hello', 'Hello'] (start of each line)

# Quantifiers
text = "a aa aaa aaaa"
print(re.findall(r'a{2,3}', text))       # ['aa', 'aaa', 'aaa']

# Alternation
text = "I have a cat and a dog"
print(re.findall(r'cat|dog', text))      # ['cat', 'dog']

# Groups
text = "abcabc abc"
print(re.findall(r'(abc)+', text))       # ['abc'] (captures last group)
print(re.findall(r'(?:abc)+', text))     # ['abcabc', 'abc'] (non-capturing)

# Escape Sequences
text = "Price: $10.99 + tax"
print(re.findall(r'\$\d+\.\d+', text))   # ['$10.99']

Common Pattern Combinations

python

# Email pattern
email_pattern = r'[\w\.-]+@[\w\.-]+\.\w+'

# Phone number pattern (basic)
phone_pattern = r'\d{3}[-.]\d{3}[-.]\d{4}'

# URL pattern (basic)
url_pattern = r'https?://(?:[-\w.]|(?:%[\da-fA-F]{2}))+'

# Date pattern (MM/DD/YYYY)
date_pattern = r'\d{2}/\d{2}/\d{4}'

Remember to use raw strings (r'pattern') for regular expressions to avoid issues with backslash escaping!

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