Some common regular expressions (regex) examples in Python

Some common regular expressions (regex) examples in Python

Matching a single character:

import re

Match any digit (0-9)
re.findall(r"\d", "abc123")

Match any lowercase letter (a-z)
re.findall(r"[a-z]", "abc123")

Match any uppercase letter (A-Z)
re.findall(r"[A-Z]", "ABC123")

Match any letter (a-z, A-Z)
re.findall(r"[a-zA-Z]", "ABC123")
Matching a specific string:

import re

Match the string "cat"
re.findall(r"cat", "The cat in the hat")

Match the string "dog"
re.findall(r"dog", "The cat in the hat")

Matching a pattern of characters:

import re

Match any string that starts with "cat"
re.findall(r"^cat", "cat in the hat")

Match any string that ends with "dog"
re.findall(r"dog$", "The cat and the dog")

Match any string that contains "hat"
re.findall(r"hat", "The cat in the hat")
Matching repeated patterns:

import re

Match any string that has two consecutive digits
re.findall(r"\d\d", "abc123")

Match any string that has three consecutive lowercase letters
re.findall(r"[a-z]{3}", "abc123")

Match any string that has three or more consecutive digits
re.findall(r"\d{3,}", "abc123")

Match any string that has two or more consecutive lowercase letters
re.findall(r"[a-z]{2,}", "abc123")
Matching optional patterns:

import re

Match any string that has an optional digit at the end
re.findall(r"\d?", "abc123")

Match any string that has an optional lowercase letter at the end
re.findall(r"[a-z]?", "abc123")

Match any string that has an optional digit at the start
re.findall(r"^\d?", "abc123")

Match any string that has an optional lowercase letter at the start
re.findall(r"^[a-z]?", "abc123")
Matching groups of patterns:

import re

Match any string that has a word (consisting of letters) followed by a digit
re.findall(r"\b\w+\b\d", "abc123")

Match any string that has a digit followed by a word (consisting of letters)
re.findall(r"\d\b\w+\b", "abc123")
Here are a few more examples:

Matching multiple patterns:

import re

Match any string that has a word (consisting of letters) followed by a digit, and then another word
re.findall(r"\b\w+\b\d\b\w+\b", "abc123def")

Matching multiple patterns:

import re

Match any string that has a digit, followed by a word (consisting of letters), followed by another digit
re.findall(r"\d\b\w+\b\d", "abc123def")

Match any string that has a word (consisting of letters) followed by a digit, or a digit followed by a word
re.findall(r"\b\w+\b\d|\d\b\w+\b", "abc123def")

Match any string that has a word (consisting of letters) followed by a digit, or a digit followed by a word, or both
re.findall(r"\b\w+\b\d|\d\b\w+\b|\b\w+\b\d\b\w+\b", "abc123def")

Matching multiple occurrences:

import re

Match any string that has three or more consecutive occurrences of the same letter
re.findall(r"(\w)\1{2,}", "abc123def")

Match any string that has three or more consecutive occurrences of the same digit
re.findall(r"(\d)\1{2,}", "abc123def")

Match any string that has two or more consecutive occurrences of the same letter, separated by a digit
re.findall(r"(\w)\d(\1)", "abc123def")

Match any string that has two or more consecutive occurrences of the same digit, separated by a letter
re.findall(r"(\d)\w(\1)", "abc123def")

Matching any character:

import re

Match any string that has a single character
re.findall(r".", "abc123def")

Match any string that has two consecutive characters
re.findall(r"..", "abc123def")

Match any string that has three consecutive characters
re.findall(r"...", "abc123def")

Match any string that has four consecutive characters
re.findall(r"....", "abc123def")

Matching any digit:

import re

Match any string that has a single digit
re.findall(r"\d", "abc123def")

Match any string that has two consecutive digits
re.findall(r"\d\d", "abc123def")

Match any string that has three consecutive digits
re.findall(r"\d\d\d", "abc123def")

Match any string that has four consecutive digits
re.findall(r"\d\d\d\d", "abc123def")

Matching any letter:

import re

Match any string that has a single letter
re.findall(r"[a-zA-Z]", "abc123def")

Match any string that has two consecutive letters
re.findall(r"[a-zA-Z][a-zA-Z]", "abc123def")

Match any string that has three consecutive letters
re.findall(r"[a-zA-Z][a-zA-Z][a-zA-Z]", "abc123def")

Matching any letter:

import re

Match any string that has four consecutive letters
re.findall(r"[a-zA-Z][a-zA-Z][a-zA-Z][a-zA-Z]", "abc123def")

Match any string that has two or more consecutive letters
re.findall(r"[a-zA-Z]{2,}", "abc123def")

Match any string that has three or more consecutive letters
re.findall(r"[a-zA-Z]{3,}", "abc123def")

Match any string that has four or more consecutive letters
re.findall(r"[a-zA-Z]{4,}", "abc123def")

Matching any word:

import re

Match any string that has a single word
re.findall(r"\b\w+\b", "abc 123 def")

Match any string that has two consecutive words
re.findall(r"\b\w+\b\s\b\w+\b", "abc 123 def")

Match any string that has three consecutive words
re.findall(r"\b\w+\b\s\b\w+\b\s\b\w+\b", "abc 123 def")

Match any string that has four consecutive words
re.findall(r"\b\w+\b\s\b\w+\b\s\b\w+\b\s\b\w+\b", "abc 123 def")

Match any string that has two or more consecutive words
re.findall(r"\b\w+\b\s{1,}\b\w+\b", "abc 123 def")

Match any string that has three or more consecutive words
re.findall(r"\b\w+\b\s{1,}\b\w+\b\s{1,}\b\w+\b", "abc 123 def")

Match any string that has four or more consecutive words
re.findall(r"\b\w+\b\s{1,}\b\w+\b\s{1,}\b\w+\b\s{1,}\b\w+\b", "abc 123 def")