Detailed Guide to Python String Processing with the re and string Modules

In Python programming, handling strings is a frequent task; this guide introduces two essential modules— re for regular expressions and string for predefined character sets—to perform matching, replacement, splitting, and validation operations.

re module

The re module offers powerful tools for text pattern matching and substitution.

Example 1: Search pattern

import re
# Search pattern
text = "Hello, my number is 123-456-7890."
pattern = r"\d{3}-\d{3}-\d{4}"
match = re.search(pattern, text)
print("Found pattern:", match.group() if match else "No match found.")

Example 2: Replace pattern

import re
# Replace pattern
text = "Hello, my number is 123-456-7890."
new_text = re.sub(r"\d{3}-\d{3}-\d{4}", "[REDACTED]", text)
print("New text:", new_text)

Example 3: Find all matches

import re
# Find all matches
text = "My numbers are 123-456-7890 and 098-765-4321."
pattern = r"\d{3}-\d{3}-\d{4}"
matches = re.findall(pattern, text)
print("Found matches:", matches)

Example 4: Split string

import re
# Split string
text = "one,two,three;four,five;six"
pattern = r"[,;]"
split_text = re.split(pattern, text)
print("Split text:", split_text)

Example 5: Replace all matches using a function

import re
# Replace all matches (using function)
def redact(match):
    return "[REDACTED]"
text = "My numbers are 123-456-7890 and 098-765-4321."
pattern = r"\d{3}-\d{3}-\d{4}"
new_text = re.sub(pattern, redact, text)
print("New text:", new_text)

string module

The string module provides a collection of useful constants such as whitespace characters, letters, and digits.

Example 6: Use constants

import string
# Use constants
print("ASCII lowercase letters:", string.ascii_lowercase)
print("ASCII uppercase letters:", string.ascii_uppercase)
print("Digits:", string.digits)

Example 7: Generate a random password

import string
import random
# Generate random password
def generate_password(length=10):
    characters = string.ascii_letters + string.digits + string.punctuation
    password = ''.join(random.choice(characters) for i in range(length))
    return password
password = generate_password()
print("Generated password:", password)

Example 8: Remove whitespace characters

import string
# Remove whitespace characters
text = "Hello,   world!"
cleaned_text = text.translate(str.maketrans("", "", string.whitespace))
print("Cleaned text:", cleaned_text)

Example 9: Check if a string contains only digits

import string
# Check if a string contains only digits
text = "1234567890"
if all(char in string.digits for char in text):
    print(f"'{text}' contains only digits.")
else:
    print(f"'{text}' does not contain only digits.")

Example 10: Check if a string contains only letters

import string
# Check if a string contains only letters
text = "HelloWorld"
if all(char in string.ascii_letters for char in text):
    print(f"'{text}' contains only letters.")
else:
    print(f"'{text}' does not contain only letters.")