Complete List of Basic Regular Expression Patterns in Python

Character Classes

Pattern	Description	Example
`[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 `\w`	Matches word characters

Predefined Character Classes

Pattern	Description	Equivalent
`.`	Matches any character except newline
`\d`	Matches any digit	`[0-9]`
`\D`	Matches any non-digit	`[^0-9]`
`\w`	Matches any word character	`[a-zA-Z0-9_]`
`\W`	Matches any non-word character	`[^a-zA-Z0-9_]`
`\s`	Matches any whitespace character	`[ \t\n\r\f\v]`
`\S`	Matches any non-whitespace character	`[^ \t\n\r\f\v]`

Anchors (Position Matchers)

Pattern	Description	Example
`^`	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
`\b`	Matches word boundary	`\bword\b` matches “word” as whole word
`\B`	Matches non-word boundary	`\Bword\B` matches “word” inside other words

Quantifiers (Repetition)

Pattern	Description	Example
`*`	0 or more occurrences	`a*` matches “”, “a”, “aa”, “aaa”, …
`+`	1 or more occurrences	`a+` matches “a”, “aa”, “aaa”, …
`?`	0 or 1 occurrence	`a?` matches “” or “a”
`{n}`	Exactly n occurrences	`a{3}` matches “aaa”
`{n,}`	n or more occurrences	`a{2,}` matches “aa”, “aaa”, “aaaa”, …
`{n,m}`	Between n and m occurrences	`a{2,4}` matches “aa”, “aaa”, “aaaa”

Alternation and Grouping

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

Escape Sequences

Pattern	Description	Example
`\\`	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

Pattern	Description	Example
`\A`	Matches only at start of string	`\AStart`
`\Z`	Matches only at end of string	`end\Z`
`\n`	Newline character
`\t`	Tab character
`\r`	Carriage return
`\f`	Form feed
`\v`	Vertical 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!

List of Basic Regular Expression Patterns in Python

Complete List of Basic Regular Expression Patterns in Python

Character Classes

Predefined Character Classes

Anchors (Position Matchers)

Quantifiers (Repetition)

Alternation and Grouping

Escape Sequences

Special Sequences

Practical Examples with Each Pattern Type

Common Pattern Combinations

re.findall()

Generalization vs. Specialization

re.compile() re.search() re.match()

re Programs

List of machine learning libraries in python

Class06,07 Operators, Expressions

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Complete List of Basic Regular Expression Patterns in Python

Character Classes

Predefined Character Classes

Anchors (Position Matchers)

Quantifiers (Repetition)

Alternation and Grouping

Escape Sequences

Special Sequences

Practical Examples with Each Pattern Type

Common Pattern Combinations

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