Strings & text
Format, split, join, parse, and clean text — everyday Python string patterns.
Automatically Detect Weak Passwords from Large Password Lists in Python
This Python script identifies weak passwords from a list by checking length, common patterns, sequential characters, and uniform characters, returning those that fail the security checks.
import re
COMMON_PASSWORDS_FILE = "common_passwords.txt"
def is_weak(password):
# Check length
if len(password) < 8:
return True
# Check for common patterns
if password.lower() in {"password", "123456", "qwerty", "letmein", "admin", "welcome"}:
return True
# Check for sequential c…Build a Secure Password Strength Checker in Python
A Python function that evaluates password strength based on length and character diversity, returning Weak, Moderate, or Strong.
import re
def password_strength(password: str) -> str:
score = 0
if len(password) >= 8:
score += 1
if re.search(r'[a-z]', password):
score += 1
if re.search(r'[A-Z]', password):
score += 1
if re.search(r'\d', password):
score += 1
if re.search(r'[!@#$%^&*(),.?":…Extract Email-Like Tokens from Text in Python
Uses a regular expression to find all email-like tokens in a string, returning them as a list with re.findall.
import re
def extract_email_like_tokens(text):
pattern = r'\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\b'
return re.findall(pattern, text)
if __name__ == "__main__":
sample_text = (
"Contact us at support@example.com or sales@company.co.uk. "
"Invalid: hello@world, user@.com, test@do…Extract URLs from text with regex in Python
Uses a regular expression to find and print HTTP/HTTPS URLs from a block of text.
import re
text = """
Visit https://www.example.com for docs.
Contact support@mysite.org.
Check http://localhost:8000/api or ftp://files.example.net.
"""
url_pattern = r'https?://[^\s]+'
urls = re.findall(url_pattern, text)
for url in urls:
print(url)Find Data From a String in Python: Stats, Clean, Keywords
Three helper functions for beginners: compute character/word/sentence stats, normalize whitespace and case, and extract unique sorted keywords from a string.
def get_text_stats(text):
"""Return basic statistics about a string."""
words = text.split()
sentences = text.replace('!', '.').replace('?', '.').split('.')
sentences = [s for s in sentences if s.strip()]
return {
'characters': len(text),
'words': len(words),
'sentences': le…Find Most Frequent Character in a String in Python
Count character frequencies in a Python string using a dictionary and return the character that appears most often with a max() key function.
def most_frequent_char(s: str) -> str:
if not s:
return ""
char_count = {}
for ch in s:
char_count[ch] = char_count.get(ch, 0) + 1
max_char = max(char_count, key=char_count.get)
return max_char
if __name__ == "__main__":
text = "programming"
result = most_frequent…Find the Index of a Substring or Return a Default in Python
Finds the index of a substring using str.find() and returns a specified default value instead of -1 when the substring is not found.
def find_substring_or_default(text, substring, default=-1):
index = text.find(substring)
return index if index != -1 else default
if __name__ == "__main__":
text = "The quick brown fox jumps over the lazy dog"
print(find_substring_or_default(text, "brown"))
print(find_substring_or_default(text, "c…Find the Longest Word in a Sentence in Python
Splits a sentence into words and returns the longest one using the built-in max() function with len as the key.
def find_longest_word(sentence: str) -> str:
words = sentence.split()
if not words:
return ""
return max(words, key=len)
if __name__ == "__main__":
test_sentence = "The quick brown fox jumps over the lazy dog"
longest = find_longest_word(test_sentence)
print(f"Longest word: '{longest}'…How to Build a Basic Text Processor in Python
Split text into sentences, count words, find the longest word, and convert text to uppercase — all with pure Python string methods.
text = """The quick brown fox jumps over the lazy dog.
Python is a powerful programming language.
Keep practicing every single day!"""
sentences = text.split(". ")
word_count = 0
longest_word = ""
for sentence in sentences:
words = sentence.split()
word_count += len(words)
for word in words:
clea…How to Check Palindrome in Python (Ignore Case and Spaces)
Check whether a string is a palindrome while ignoring case, spaces, and all non-alphanumeric characters using Python's filter and string reversal.
def is_palindrome(text: str) -> bool:
cleaned = ''.join(char.lower() for char in text if char.isalnum())
return cleaned == cleaned[::-1]
if __name__ == "__main__":
test_cases = [
"A man, a plan, a canal: Panama",
"race a car",
"Was it a car or a cat I saw?",
"hello",
…How to Check and Manipulate Strings in Python
Demonstrates core string inspection and transformation methods like case conversion, trimming, splitting, and membership checks on a sample string.
text = " Hello, Python Learners! "
print(f"Original: '{text}'")
print(f"Lowercase: '{text.lower()}'")
print(f"Uppercase: '{text.upper()}'")
print(f"Title case: '{text.title()}'")
print(f"Stripped: '{text.strip()}'")
print(f"Length: {len(text)}")
print(f"Replace: '{text.replace('Python', 'Programming')}'")
print(f"S…How to Check if a String Starts With a Prefix Case-Insensitively in Python
This code defines a function that checks if a string starts with a given prefix, ignoring case, using the lower() method.
def starts_with_case_insensitive(text, prefix):
"""Check if a string starts with a given prefix, ignoring case."""
return text.lower().startswith(prefix.lower())
if __name__ == "__main__":
test_strings = [
("Hello World", "hello"),
("Python Programming", "PYTHON"),
("Data Science"…How to Check if a String is Numeric in Python
This code provides a function to determine if a string represents a valid numeric value using Python's built-in float() conversion.
def is_numeric(s):
"""Check if a string represents a valid numeric value."""
try:
float(s)
return True
except (ValueError, TypeError):
return False
if __name__ == "__main__":
test_cases = ["123", "-45.67", "3.14e10", "0x1A", "abc", "12.5.6", " 42 ", ""]
for case in test_c…How to Compare Strings with casefold in Python
Compares two strings ignoring case differences using the casefold() method for proper Unicode normalization.
def compare_strings(str1: str, str2: str) -> bool:
return str1.casefold() == str2.casefold()
if __name__ == "__main__":
tests = [
("HELLO", "hello"),
("Straße", "STRASSE"),
("Python", "Python"),
("Mixed Case", "mixed case"),
]
for s1, s2 in tests:
print(f"{s1!r}…How to Compare Two Strings in Python
Compares two string values and returns a detailed report with equality, case-insensitive comparison, lengths, and uppercase versions.
def compare_data(first_value, second_value):
"""Compare two string values and return a report."""
if first_value == second_value:
status = "MATCH"
else:
status = "DIFFER"
return {
"first_value": first_value,
"second_value": second_value,
"status": status,
…How to Convert Data to Strings in Python
Convert common data types like bytes, numbers, containers, and None to readable strings with a safe helper function.
def to_str(value):
"""Convert common types to a readable string, safe for beginners."""
if isinstance(value, bytes):
return value.decode("utf-8")
if isinstance(value, (dict, list, tuple, set)):
return str(value)
if value is None:
return ""
return str(value)
if __name__ == …How to Convert and Process Text in Python
This code cleans, converts, splits, joins, counts, replaces, reverses, and finds substrings in a text string using Python's standard string methods.
text = " hello world, python is fun! "
# Clean up whitespace
cleaned = text.strip()
# Convert to title case
titled = cleaned.title()
# Split into words
words = cleaned.split()
# Join with hyphens
hyphenated = "-".join(words)
# Count occurrences of a letter
letter_count = cleaned.count("o")
# Replace a word
rep…How to Convert camelCase to snake_case in Python
Convert camelCase strings to snake_case using a simple Python function that inserts underscores before uppercase letters and lowercases everything.
def camel_to_snake(s):
result = ""
for i, char in enumerate(s):
if char.isupper() and i > 0:
result += "_"
result += char.lower()
return result
if __name__ == "__main__":
test_cases = ["camelCase", "helloWorld", "thisIsACoolExample", "already_snake", "UPPER"]
for case i…How to Convert snake_case to Title Case in Python
Convert snake_case strings to title case by splitting on underscores, capitalizing each word, and joining them with spaces.
def to_title_case(snake_str):
words = snake_str.split("_")
return " ".join(word.capitalize() for word in words)
if __name__ == "__main__":
examples = ["hello_world", "convert_snake_case", "already_title_case", "multiple__under_scores"]
for example in examples:
print(f"{example!r:35} -> {to_tit…How to Count Vowels in a String in Python
Counts uppercase and lowercase vowels in a given string using a set and a generator expression.
def count_vowels(text):
vowels = set("aeiouAEIOU")
return sum(1 for char in text if char in vowels)
if __name__ == "__main__":
sample = "Hello, World!"
result = count_vowels(sample)
print(f"Vowel count in '{sample}': {result}")How to Count Words in a String in Python
Split a paragraph on whitespace and return the number of words using Python's built-in string methods.
def count_words(paragraph: str) -> int:
words = paragraph.split()
return len(words)
if __name__ == "__main__":
paragraph = "The quick brown fox jumps over the lazy dog."
result = count_words(paragraph)
print(f"Word count: {result}")How to Detect Expired Domains Using Python
Parse a list of domain registration data and compare expiry dates to today to find expired domains.
import datetime
# List of test domains with fake registration and expiry dates
# Format: (domain, registration_date, expiry_date)
test_domains = [
('example.com', '2020-01-15', '2024-01-15'), # Expired
('google.com', '1997-09-15', '2026-09-15'), # Still active
('test-site.org', '2019-06-01', '2023-06-0…How to Detect PII in Documents Using Python
Use regex patterns to automatically detect emails, phone numbers, SSNs, and credit card numbers in text documents.
import re
from typing import List, Dict
def detect_pii(text: str) -> Dict[str, List[str]]:
patterns = {
"email": r"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}",
"phone": r"\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}",
"ssn": r"\b\d{3}-\d{2}-\d{4}\b",
"credit_card": r"\b\d{4}[- ]?\d{4}[-…How to Escape HTML in Python
This code demonstrates how to use Python's `html.escape` function to safely encode user input for display in HTML, preventing XSS attacks.
import html
def escape_user_input(user_input: str) -> str:
"""Escape HTML-sensitive characters for safe display."""
return html.escape(user_input)
if __name__ == "__main__":
sample_user_input = '<script>alert("XSS")</script> & \'quotes\''
safe_output = escape_user_input(sample_user_input)
print("…Browse by section
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Strings & text — Python code examples
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This page collects strings & text snippets — short, copy-ready Python you can paste into our free online IDE and run without installing anything. Each sample includes a plain-English explanation and the full source code.
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Samples are quick reference — one concept per page. For step-by-step teaching, use our Python tutorials. To test yourself, try quizzes or coding challenges. Clean up style with the Python formatter.