How to Use Regular Expressions in python with the re Module

Using Regular Expressions in Python with (re) Module

The built-in re-module makes regular expressions (regex) in Python easy. Regular expressions are powerful tools for matching, searching, and manipulating text. Here’s a guide on how to use the re-module in Python.

1. Importing the re-module 

 

import re

 

Here  are commonly used methods in the re-module

1. re.match()

The re.match() function checks for a match only at the beginning of the string.

import re
pattern = r"hello"
text = "hello world"
match = re.match(pattern, text)
if match:
    print("Match found:",match.group())
else:
   print("No match")

Output:

Match found: hello

2. re.search()

The research function searches for the first occurrence of the pattern anywhere in the string.

import re 
pattern = r"world"
text ="hello world "
match = re.search(pattern , text)
if match:
    print("Found:", match.group())
else:
    print("Not found")

Output:

Found: world

3. re. findall()

The re. findall function is used to find all occurrences of the pattern and return them as a list

import re 
pattern ="\d+"
text = "I have 2 apples and 3 bananas."
matches = re.findall(pattern, text)
print("Matches:", matches)

Output:

Matches:['2', '3']

3. re.finditer()

The re. funditer function Returns an iterator of match objects for all occurrences.

import re 
pattern = r"\W+"
text ="python is fun !"
matches = re.finditer(pattern, text)
for match in matches:
    print("Match:", match.group())

Output:

Match:

Match:

Match: !

4. re. sub()

Replaces occurrences of a pattern with a specified string.

import re 
pattern = r"\s+"
text ="python is fun"
result = re.sub(pattern," ",text)
print("Result:", result)

Output:

Result : python is fun

Pattern syntax

• .  : Matches any character (except newline).
• ^: Matches the start of the string.
• $: Matches the end of the string.
• *: Matches 0 or more repetitions.
• +: Matches 1 or more repetitions.
• ?: Matches 0 or 1 repetition.
• {n,m}: Matches between n and m repetitions.
• []: Matches any character inside the brackets.
• |: Logical OR
• \: Escapes special characters

5. Flags

you can use flags to modify regex behavior:

• re.IGNORECASE or re.I: Case-insensitive matching.
• re.MULTILINE or re.M: Matches across multiple lines.
• re.DOTALL or re.S: . Matches the newline as well.

Example with a flag:

import re 
pattern =r"python "
text = "python is amazing"
match = re.search(pattern, text, re.IGNORECASE)
if match:
    print("Match found :", match.group())

Output:

Match found : python

6. compiling regular expressions

For efficiency, you can compile a pattern to reuse it.

import re
pattern = re.compile(r"\d+")
text = "There are 12 eggs and 34 apples."
matches = pattern.findall(text)
print("Matches:", matches")

Output:

Matches:['12', '34']

7. Practical Example

Extracting email addresses:

import re 
text = "contact us at [email protected] or [email protected]"
pattern = r"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}"
emails = re.findall(pattern,text)
print("Emails found:", emails)

Output:

Emails found :['[email protected]', '[email protected]']