Python Strings Complete Guide

# Single quotes
name = 'John Doe'

# Double quotes
message = "Hello World"

# Triple quotes (multi-line strings)
paragraph = """This is a
multi-line string
spanning multiple lines"""

# Using single quotes inside double quotes
text = "It's a beautiful day"

# Using double quotes inside single quotes
text2 = 'He said "Hello" to me'

# Empty string
empty = ""

# Strings from other types
number_str = str(123)        # "123"
float_str = str(3.14159)     # "3.14159"
bool_str = str(True)         # "True"

text = "Python"

# Positive indexing (0-based)
print(text[0])    # P
print(text[1])    # y
print(text[3])    # h

# Negative indexing (from end)
print(text[-1])   # n (last character)
print(text[-2])   # o
print(text[-3])   # h

# Strings are immutable - this causes error
# text[0] = 'J'  # TypeError: 'str' object does not support item assignment

text = "Programming"

# Syntax: [start:end:step]
# start - included, end - excluded

print(text[0:4])     # "Prog" (indices 0,1,2,3)
print(text[4:8])     # "rami"
print(text[:4])      # "Prog" (from start)
print(text[4:])      # "ramming" (to end)
print(text[:])       # "Programming" (full copy)
print(text[::2])     # "Pormig" (every 2nd character)
print(text[1::2])    # "rgamn" (every 2nd starting from index 1)

# Negative slicing
print(text[-4:])     # "ming" (last 4 characters)
print(text[-8:-4])   # "gram"
print(text[::-1])    # "gnimmargorP" (reverse string)

# Using + operator
greeting = "Hello" + " " + "World"
print(greeting)  # "Hello World"

# Using join() method
words = ["Python", "is", "awesome"]
sentence = " ".join(words)
print(sentence)  # "Python is awesome"

# Using * operator
stars = "*" * 10
print(stars)     # "**********"

line = "-=" * 5
print(line)      # "-=-=-=-=-="

text = "Python Programming"
print(len(text))  # 19 (including space)

text = "Hello World"

print("Hello" in text)    # True
print("hello" in text)    # False (case sensitive)
print("XYZ" not in text)  # True

# String comparison is lexicographic (dictionary order)
print("apple" < "banana")    # True (a comes before b)
print("Apple" < "apple")     # True (uppercase < lowercase in ASCII)
print("abc" == "abc")        # True
print("abc" != "def")        # True

text = "python Programming TUTORIAL"

print(text.upper())      # "PYTHON PROGRAMMING TUTORIAL"
print(text.lower())      # "python programming tutorial"
print(text.capitalize()) # "Python programming tutorial"
print(text.title())      # "Python Programming Tutorial"
print(text.swapcase())   # "PYTHON pROGRAMMING tutorial"

# Check case
print("HELLO".isupper())    # True
print("hello".islower())    # True
print("Hello".istitle())    # True

text = "The quick brown fox jumps over the lazy dog"

# Find (returns index or -1)
print(text.find("fox"))      # 16
print(text.find("cat"))      # -1
print(text.rfind("the"))     # 35 (search from right)

# Index (like find but raises ValueError if not found)
print(text.index("fox"))     # 16
# print(text.index("cat"))   # ValueError

# Count occurrences
print(text.count("o"))       # 4
print(text.count("the"))     # 1

# Replace
print(text.replace("fox", "cat"))     # "The quick brown cat jumps over the lazy dog"
print(text.replace(" ", "_"))         # "The_quick_brown_fox_jumps_over_the_lazy_dog"
print(text.replace("o", "0", 2))      # "The quick br0wn f0x jumps over the lazy dog"

text = "   Hello World   "

print(text.strip())      # "Hello World" (removes both ends)
print(text.lstrip())     # "Hello World   " (removes left)
print(text.rstrip())     # "   Hello World" (removes right)

text2 = "---Python---"
print(text2.strip("-"))  # "Python"

# Split
text = "apple,banana,orange,grape"
fruits = text.split(",")
print(fruits)  # ['apple', 'banana', 'orange', 'grape']

text2 = "one two three four"
words = text2.split()
print(words)   # ['one', 'two', 'three', 'four']

text3 = "a,b,c,d"
print(text3.split(",", 2))  # ['a', 'b', 'c,d'] (split 2 times)

# Partition - splits at first occurrence
text4 = "name:John"
print(text4.partition(":"))  # ('name', ':', 'John')
print(text4.rpartition(":")) # ('name', ':', 'John') (from right)

# Join
delimiter = "-"
result = delimiter.join(["2024", "12", "25"])
print(result)  # "2024-12-25"

words = ["Python", "is", "fun"]
sentence = " ".join(words)
print(sentence)  # "Python is fun"

# Alphanumeric checks
print("Hello123".isalnum())    # True (letters and numbers)
print("Hello 123".isalnum())   # False (space not allowed)
print("Hello".isalpha())       # True (only letters)
print("12345".isdigit())       # True (only digits)
print("123abc".isdigit())      # False
print("    ".isspace())        # True (only whitespace)

# Other checks
print("Hello".isascii())       # True (ASCII characters)
print("Hello123".isidentifier()) # True (valid Python identifier)
print("123".isdecimal())       # True (decimal numbers)
print("一二三".isnumeric())     # True (numeric characters)

text = "Python"

# Center
print(text.center(20))          # "      Python       "
print(text.center(20, "*"))     # "*******Python*******"

# Left align
print(text.ljust(20))           # "Python              "
print(text.ljust(20, "-"))      # "Python--------------"

# Right align
print(text.rjust(20))           # "              Python"
print(text.rjust(20, "-"))      # "--------------Python"

# Zero fill
print("42".zfill(5))            # "00042"
print("-42".zfill(5))           # "-0042"

name = "Alice"
age = 30
height = 5.6

# Basic f-string
print(f"Name: {name}, Age: {age}")  # "Name: Alice, Age: 30"

# Expressions inside {}
print(f"Next year: {age + 1}")       # "Next year: 31"
print(f"Square of 5: {5**2}")         # "Square of 5: 25"

# Formatting numbers
print(f"Pi: {3.14159:.2f}")          # "Pi: 3.14"
print(f"Percentage: {0.75:.1%}")      # "Percentage: 75.0%"
print(f"Number: {42:05d}")           # "Number: 00042"

# Alignment
print(f"{'Left':<10}")    # "Left      "
print(f"{'Right':>10}")   # "     Right"
print(f"{'Center':^10}")  # "  Center  "

# Positional arguments
print("{} {} {}".format("Python", "is", "fun"))     # "Python is fun"
print("{1} {0} {2}".format("Python", "is", "fun"))  # "is Python fun"

# Keyword arguments
print("{name} is {age} years old".format(name="Bob", age=25))

# Dictionary unpacking
data = {"name": "Charlie", "age": 35}
print("{name} is {age} years old".format(**data))

# Formatting specifiers
print("{:.2f}".format(3.14159))    # "3.14"
print("{:05d}".format(42))         # "00042"
print("{:>10}".format("right"))    # "     right"

# %s - string, %d - integer, %f - float
name = "David"
age = 28
height = 5.9

print("Name: %s, Age: %d" % (name, age))           # "Name: David, Age: 28"
print("Height: %.2f" % height)                    # "Height: 5.90"
print("Hex: %x" % 255)                            # "Hex: ff"

# Common escape sequences
print("Hello\nWorld")     # New line
print("Hello\tWorld")     # Tab
print("Hello\\World")     # Backslash
print("Hello\"World\"")   # Double quote
print("Hello\'World\'")   # Single quote
print("Hello\rWorld")     # Carriage return
print("Hello\bWorld")     # Backspace
print("Hello\fWorld")     # Form feed

# Raw strings (ignore escape sequences)
print(r"C:\Users\Name\Documents")  # "C:\Users\Name\Documents"
print(r"Hello\nWorld")             # "Hello\nWorld" (not line break)

# Raw strings are prefixed with 'r' or 'R'
# They treat backslashes as literal characters

# Normal string
normal = "C:\\Users\\Name\\file.txt"

# Raw string (cleaner)
raw = r"C:\Users\Name\file.txt"

print(normal)  # "C:\Users\Name\file.txt"
print(raw)     # "C:\Users\Name\file.txt"

# Useful for regex patterns
import re
pattern = r"\d+"  # Matches one or more digits

text = "Python"

# Method 1: Direct iteration
for char in text:
    print(char)

# Method 2: With index
for i in range(len(text)):
    print(f"Index {i}: {text[i]}")

# Method 3: enumerate
for i, char in enumerate(text):
    print(f"Index {i}: {char}")

filename = "document.pdf"
url = "https://python.org"

print(filename.startswith("doc"))    # True
print(filename.endswith(".pdf"))     # True
print(url.startswith("https"))       # True

# With tuple of options
print(filename.endswith((".txt", ".pdf", ".doc")))  # True

# Get ASCII/Unicode value
print(ord('A'))    # 65
print(ord('a'))    # 97

# Get character from ASCII value
print(chr(65))     # 'A'
print(chr(97))     # 'a'

text = "Python"

# Using slicing
reversed_text = text[::-1]
print(reversed_text)  # "nohtyP"

# Using reversed() and join
reversed_text2 = ''.join(reversed(text))
print(reversed_text2)  # "nohtyP"

def validate_email(email):
    # Check for @ and .
    if '@' not in email or '.' not in email:
        return False
    
    # Split into local and domain parts
    local, domain = email.split('@')
    
    # Check conditions
    if len(local) == 0 or len(domain) < 3:
        return False
    
    if '.' not in domain:
        return False
    
    return True

print(validate_email("user@example.com"))    # True
print(validate_email("invalid-email"))       # False

def check_password_strength(password):
    score = 0
    feedback = []
    
    # Length check
    if len(password) >= 8:
        score += 1
    else:
        feedback.append("Password should be at least 8 characters")
    
    # Contains uppercase
    if any(char.isupper() for char in password):
        score += 1
    else:
        feedback.append("Add uppercase letters")
    
    # Contains lowercase
    if any(char.islower() for char in password):
        score += 1
    else:
        feedback.append("Add lowercase letters")
    
    # Contains digits
    if any(char.isdigit() for char in password):
        score += 1
    else:
        feedback.append("Add numbers")
    
    # Contains special characters
    special_chars = "!@#$%^&*"
    if any(char in special_chars for char in password):
        score += 1
    else:
        feedback.append("Add special characters")
    
    # Rating
    if score == 5:
        rating = "Strong"
    elif score >= 3:
        rating = "Medium"
    else:
        rating = "Weak"
    
    return rating, feedback

password = "Python@123"
rating, feedback = check_password_strength(password)
print(f"Password strength: {rating}")
if feedback:
    print("Suggestions:")
    for tip in feedback:
        print(f"  - {tip}")

def wrap_text(text, width=50):
    """Wrap text to specified width"""
    words = text.split()
    lines = []
    current_line = []
    current_length = 0
    
    for word in words:
        if current_length + len(word) + 1 <= width:
            current_line.append(word)
            current_length += len(word) + 1
        else:
            lines.append(' '.join(current_line))
            current_line = [word]
            current_length = len(word) + 1
    
    if current_line:
        lines.append(' '.join(current_line))
    
    return '\n'.join(lines)

long_text = """Python is an interpreted high-level general-purpose programming language. 
Its design philosophy emphasizes code readability with its use of significant indentation."""

wrapped = wrap_text(long_text, 40)
print(wrapped)

def custom_title(text):
    """Convert string to title case without using title()"""
    result = []
    new_word = True
    
    for char in text:
        if char.isspace():
            result.append(char)
            new_word = True
        else:
            if new_word:
                result.append(char.upper())
                new_word = False
            else:
                result.append(char.lower())
    
    return ''.join(result)

print(custom_title("hello world"))        # "Hello World"
print(custom_title("python is FUN"))      # "Python Is Fun"

def is_palindrome(text):
    # Remove spaces and convert to lowercase
    cleaned = ''.join(text.lower().split())
    
    # Check if equals its reverse
    return cleaned == cleaned[::-1]

# Test
words = ["racecar", "hello", "A man a plan a canal panama", "Python"]
for word in words:
    print(f"'{word}' is palindrome: {is_palindrome(word)}")

# Strings are immutable
text = "Hello"
# text[0] = "J"  # ERROR!

# Create new string instead
text = "J" + text[1:]  # "Jello"

# Case sensitivity
print("Hello".find("hello"))  # -1 (not found)

# strip() removes from both ends only
text = "  Hello World  "
print(text.strip())        # "Hello World"
print(text.replace(" ", ""))  # "HelloWorld"