Re Module

Last Updated: 22th August 2025

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The re module is used for working with regular expressions in Python. It allows you to search, match, and manipulate text using patterns.

Patterns are:

Symbol	Description	Example	Matches
^	Matches the start of the string or line	^Hello	Hello there (start match)
$	Matches the end of the string or line	end$	The end (end match)
{m}	Matches exactly m repetitions of the preceding element	a{3}	aaa
{m,}	Matches at least m repetitions of the preceding element	a{2,}	aa, aaa
{(m, n)}	Matches between m and n repetitions	a{(2, 4)}	aa, aaa, aaaa
( ... )	Groups patterns or captures matched substring	(ab)+	ab, abab, ababab
|	OR operator: matches either pattern on left or right	cat|dog	cat or dog
[abc]	Character class: matches any one character listed	[aeiou]	any vowel
[^abc]	Negated character class: matches any character not listed	[^0-9]	any non-digit character
\	Escape character: matches a literal backslash or special char	\.	a literal dot .
.	Matches any single character except newline	a.b	aab, acb, a9b
*	Matches zero or more repetitions of the previous character	ca*t	ct, cat, caaaat
+	Matches one or more repetitions of the previous character	go+gle	gogle, google, gooogle
?	Matches zero or one repetition (makes preceding optional)	colou?r	color, colour
\b	Matches a word boundary	\bcat\b	cat but not cats or cat.
\d	Matches any digit (0-9)	\d{}	123, 456, 007
\D	Matches any non-digit character	\D+	abc, !@#
\w	Matches any alphanumeric character or underscore	\w+	hello123, _var
\W	Matches any non-word character	\W+	!@#, spaces
\s	Matches any whitespace character (space, tab, newline)	\s+	space, tab, newline
\S	Matches any non-whitespace character	\S+	hello, 123

List of Functions:

• re.match(pattern, string): searches for a match at the beginning of the string.

import re
text = "123abc"
dataObj = re.match(r"\d+", text)
if match:
    print(dataObj.group()) # Output: "123"
    print(dataObj.start()) # Output: 0,start position of matched string
    print(dataObj.end())   # Output: 3,end position of matched string

• re.search(pattern, string): searches for a match anywhere in the string.

import re
text = "Order number: 12345"
dataObj = re.search(r"\d+", text)
print(dataObj.group())
# Output: "12345"

• flags: re.I,re.M,re.S etc.

import re

text = """Apple
banana
cherry
apple
banana
fruit\\nList
"""

print(re.findall(r"apple", text, re.I))      # ['Apple', 'apple'] ignoring case
print(re.findall(r"^b", text, re.M))         # ['b', 'b']  multiple lines
print(re.findall(r"apple.*", text, re.S))    # ['apple\nbanana\nfruit\\nList\n'] ignoring newlines

• re.findall(pattern, string): returns a list of all matches in the string.

import re
text = "apple 123, banana 456, cherry 789"
numbers = re.findall(r"\d+", text)
print(numbers)
# Output: ["123", "456", "789"]

• re.finditer(pattern, string): returns an iterator over all matches in the string.

import r
text = "A1 B22 C333"
for dataObj in re.finditer(r"\d+", text):
    print(dataObj.group(), "at position", dataObj.start(), "-", dataObj.end())

# Output:
#1 at position 1 - 2
#22 at position 3 - 5
#333 at position 6 - 9

• re..sub(pattern, replacement, string): replaces all matches with the replacement string.

import re
text = "I have 2 apples and 3 bananas"
new_text = re.sub(r"\d+", "#", text)
print(new_text)
# Output: "I have # apples and # bananas"

• re.split(pattern, string): splits the string into a list of substrings based on the pattern.

import re
text = "word1, word2; word3:word4"
parts = re.split(r"[,;:]\s*", text)
print(parts)
# Output: ['word1', 'word2', 'word3', 'word4']

• re.compile(pattern): creates a regex object you can reuse for multiple matches.r"..." = raw string (special characters not escaped by Python).

import re
pattern = re.compile(r"\d+")   # match one or more digits
result = pattern.findall("My number is 123 and pin is 4567")
print(result)
# Output: ['123', '4567']

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