String Manipulation & Formatting

text = "Python"

# Positive indexing (0-based, from left)
print(text[0])
print(text[1])
print(text[5])

# Negative indexing (from right)
print(text[-1])   # last character
print(text[-2])
print(text[-6])   # same as text[0]

# IndexError if out of range
try:
    text[10]
except IndexError as e:
    print(f"IndexError: {e}")

text = "Python Programming"
#       0123456789...

# Basic slicing [start:end] (end is exclusive)
print(text[0:6])
print(text[7:18])

# Omit start or end
print(text[:6])     # start defaults to 0
print(text[7:])     # end defaults to length
print(text[:])      # full copy

# Negative indices in slicing
print(text[-11:])   # last 11 characters
print(text[:-12])   # everything except last 12

text = "Python Programming"

# Step parameter [start:end:step]
print(text[::2])    # every 2nd character
print(text[::3])    # every 3rd character
print(text[1::2])   # start at index 1, every 2nd

# Reverse string with negative step
print(text[::-1])   # reverse entire string
print(text[::-2])   # reverse, every 2nd char

# Combine start, end, and step
print(text[7::2])   # start at 7, every 2nd char

text = "Hello, World!"

# First n characters
print(text[:5])
print(text[:3])

# Last n characters
print(text[-6:])
print(text[-1:])

# Remove first n characters
print(text[7:])     # skip first 7
print(text[2:])     # skip first 2

# Remove last n characters
print(text[:-7])    # remove last 7
print(text[:-1])    # remove last 1

# Reverse a string
print(text[::-1])

# Every other character
print(text[::2])

# Middle portion
print(text[2:10])

name = "Alice"
age = 30

# Basic f-string
print(f"My name is {name}")

# Multiple variables
print(f"I'm {name}, {age} years old")

# Expressions inside f-strings
print(f"Next year I'll be {age + 1}")
print(f"2 + 2 = {2 + 2}")

# Method calls inside f-strings
print(f"Hello, {name.upper()}!")

# Formatting numbers
price = 19.99
print(f"Price: ${price:.2f}")

percentage = 0.156
print(f"Score: {percentage:.1%}")

# Decimal places for floats
pi = 3.14159
print(f"{pi:.2f}")       # 2 decimal places
print(f"{pi:.4f}")       # 4 decimal places
print(f"{pi:.0f}")       # no decimal places, rounds

# Padding and alignment (the pipes make the padding visible)
name = "Bob"
print(f"|{name:>10}|")   # right align, width 10
print(f"|{name:<10}|")   # left align, width 10
print(f"|{name:^10}|")   # center, width 10
print(f"|{name:*^10}|")  # center with * padding

# Numbers with padding
num = 42
print(f"|{num:05d}|")    # pad with zeros, width 5
print(f"|{num:5d}|")     # pad with spaces, width 5

# Thousands separator
print(f"{1000000:,}")
print(f"{1234567.89:,.2f}")

# Percentage formatting
ratio = 0.75
print(f"{ratio:.1%}")
print(f"{ratio:.0%}")

# Binary, octal, hexadecimal
print(f"{num:b}")        # binary
print(f"{num:o}")        # octal
print(f"{num:x}")        # hexadecimal
print(f"{num:X}")        # uppercase hex

name = "Alice"
age = 30

# Positional arguments
print("My name is {} and I'm {} years old".format(name, age))

# Named arguments
print("My name is {n} and I'm {a} years old".format(n=name, a=age))

# Index-based (reuse arguments)
print("{0} is {1} years old. {0} is a developer.".format(name, age))

# With format specifiers
print("Price: ${:.2f}".format(19.99))
print("{:<10} | {:>10}".format("Name", "Score"))

# Reusable format strings
template = "Hello, {name}! Your score is {score:.1f}."
print(template.format(name="Bob", score=95.6))
print(template.format(name="Alice", score=87.3))

name = "Alice"
age = 30

# Old style (C-like formatting)
print("My name is %s and I'm %d years old" % (name, age))

# Format specifiers:
# %s = string
# %d = integer
# %f = float
# %.<precision>f = float with decimal places

print("Price: $%.2f" % 19.99)
print("Score: %d%%" % 85)   # need %% for a literal %

# With padding
print("%-10s | %10s" % ("Name", "Score"))

text = "hello, World!"

print(text.upper())
print(text.lower())
print(text.capitalize())   # first letter only
print(text.title())        # each word capitalized
print(text.swapcase())     # swap case

# Practical use cases
email = "Alice.Smith@EXAMPLE.com"
print(email.lower())

title = "the lord of the rings"
print(title.title())

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

text = "  Hello, World!  "

# repr() shows the quotes, so you can see exactly which spaces survive
print(repr(text.strip()))    # both ends
print(repr(text.lstrip()))   # left only
print(repr(text.rstrip()))   # right only

# Remove specific characters
print(repr("...Hello...".strip(".")))
print(repr("---555-1234---".strip("-")))

# Practical use case: cleaning user input
user_input = "  alice@example.com  "
print(repr(user_input.strip()))

# Check for whitespace
print("   ".isspace())   # all whitespace
print("abc".isspace())
print("".isspace())      # empty string

text = "Hello, World! Hello, Python!"

# Find substring (returns index or -1 if not found)
print(text.find("World"))
print(text.find("Python"))
print(text.find("Java"))       # not found
print(text.find("Hello", 1))   # search starting at index 1

# Index (like find, but raises ValueError if not found)
print(text.index("World"))
try:
    text.index("Java")
except ValueError as e:
    print(f"ValueError: {e}")

# Count occurrences
print(text.count("Hello"))
print(text.count("o"))
print(text.count("z"))

# Check start/end
print(text.startswith("Hello"))
print(text.startswith("Hi"))
print(text.endswith("Python!"))
print(text.endswith("World"))

# Check if substring exists (using 'in')
print("World" in text)
print("Java" in text)

# Case-insensitive search
print(text.lower().find("hello"))
print("hello" in text.lower())

text = "Hello, World!"

# Replace substring
print(text.replace("World", "Python"))
print(text.replace("l", "L"))
print(text.replace("l", "L", 2))     # max 2 replacements

# Remove substring (replace with empty string)
print(text.replace("Hello, ", ""))

# Split into list
print(text.split(","))
print("a-b-c".split("-"))
print("one two three".split())       # split on any whitespace

csv = "Alice,30,Engineer"
name, age, job = csv.split(",")      # unpack directly
print(name, age, job)

# Join list into string
words = ["Hello", "World"]
print(" ".join(words))
print("-".join(words))
print("".join(words))

# Join with newlines
lines = ["Line 1", "Line 2", "Line 3"]
print("\n".join(lines))

# Practical: build CSV
data = ["Alice", "30", "Engineer"]
print(",".join(data))

# Check string content type
print("123".isdigit())          # all digits
print("abc".isalpha())          # all letters
print("abc123".isalnum())       # letters or digits
print("   ".isspace())          # all whitespace
print("".isspace())             # empty string

print("Hello123".isdigit())     # has letters
print("Hello World".isalpha())  # has space

# Check case
print("Hello".istitle())
print("HeLLo".istitle())

# Practical validation examples
age_input = "25"
if age_input.isdigit():
    age = int(age_input)
    print(f"Age: {age}")
else:
    print("Invalid age - must be digits only")

username = "alice123"
if username.isalnum():
    print("Valid username")
else:
    print("Username must be alphanumeric")

# Other useful checks
print("abc".isascii())          # all ASCII characters
print("123.45".isdecimal())     # the dot is not a decimal digit
print("Hello".isprintable())

# Clean and validate email input
email = "  Alice.Smith@EXAMPLE.COM  "

# Step 1: Remove whitespace
email = email.strip()  # "Alice.Smith@EXAMPLE.COM"

# Step 2: Convert to lowercase (emails are case-insensitive)
email = email.lower()  # "alice.smith@example.com"

# Step 3: Validate structure
has_at = "@" in email
only_one_at = email.count("@") == 1

# Check domain has a dot
domain = email.split("@")[1] if has_at else ""
has_dot_in_domain = "." in domain

if has_at and only_one_at and has_dot_in_domain:
    print(f"Valid email: {email}")

    # Extract parts
    username, domain = email.split("@")
    print(f"Username: {username}")
    print(f"Domain: {domain}")

    # Check domain
    if domain.endswith(".edu"):
        print("Educational institution")
    elif domain.endswith(".com"):
        print("Commercial domain")
else:
    print("Invalid email format")

# Chain all cleaning steps
def clean_email(email):
    return email.strip().lower()

print(clean_email("  BOB@EXAMPLE.COM  "))

# Format names consistently
full_name = "  alice   marie   SMITH  "

# Step 1: Strip outer whitespace
full_name = full_name.strip()  # "alice   marie   SMITH"

# Step 2: Split by whitespace (handles multiple spaces)
parts = full_name.split()      # ["alice", "marie", "SMITH"]

# Step 3: Capitalize each part
parts = [part.capitalize() for part in parts]
# ["Alice", "Marie", "Smith"]

# Step 4: Join back together
formatted = " ".join(parts)
print(f"Formatted name: {formatted}")

# As a reusable function
def format_name(name):
    """Format a name with proper capitalization and spacing."""
    return " ".join(part.capitalize() for part in name.strip().split())

# Test the function
print(format_name("  john    DOE  "))
print(format_name("mary-jane watson"))  # capitalize() lowercases the rest

# Handle different name formats
def get_initials(name):
    """Get initials from a name."""
    parts = name.strip().split()
    initials = [part[0].upper() for part in parts]
    return ".".join(initials) + "."

print(get_initials("Alice Marie Smith"))
print(get_initials("john doe"))

# Generate a formatted sales report
name = "Alice"
items_sold = 47
revenue = 2350.75
target = 2000

# Create report with formatting
header = "Sales Report".center(40, "=")
separator = "=" * 40

report = f"""
{header}
{separator}
Salesperson: {name}
Items Sold:  {items_sold:>10}
Revenue:     ${revenue:>10,.2f}
Target:      ${target:>10,.2f}
Performance: {(revenue/target):>10.1%}
{separator}
Status:      {"EXCEEDS TARGET" if revenue > target else "BELOW TARGET"}
"""

print(report)

# Create a table
def create_table(headers, rows):
    """Create a simple text table."""
    # Calculate column widths
    col_widths = [len(h) for h in headers]
    for row in rows:
        for i, cell in enumerate(row):
            col_widths[i] = max(col_widths[i], len(str(cell)))

    # Create separator
    separator = "+" + "+".join("-" * (w + 2) for w in col_widths) + "+"

    # Header row
    header_row = "| " + " | ".join(
        h.ljust(col_widths[i]) for i, h in enumerate(headers)
    ) + " |"

    # Data rows
    data_rows = []
    for row in rows:
        data_row = "| " + " | ".join(
            str(cell).ljust(col_widths[i]) for i, cell in enumerate(row)
        ) + " |"
        data_rows.append(data_row)

    # Combine all parts
    result = [separator, header_row, separator]
    result.extend(data_rows)
    result.append(separator)

    return "\n".join(result)

# Use the table function
headers = ["Name", "Score", "Grade"]
rows = [
    ["Alice", "95", "A"],
    ["Bob", "87", "B"],
    ["Charlie", "92", "A"],
]

print(create_table(headers, rows))

def validate_password(password):
    """
    Validate password meets security requirements:
    - At least 8 characters
    - Contains uppercase and lowercase
    - Contains at least one digit
    - Contains at least one special character
    """
    errors = []

    # Check length
    if len(password) < 8:
        errors.append("Password must be at least 8 characters")

    # Check for uppercase
    if not any(c.isupper() for c in password):
        errors.append("Password must contain at least one uppercase letter")

    # Check for lowercase
    if not any(c.islower() for c in password):
        errors.append("Password must contain at least one lowercase letter")

    # Check for digit
    if not any(c.isdigit() for c in password):
        errors.append("Password must contain at least one digit")

    # Check for special character
    special_chars = "!@#$%^&*()_+-=[]{}|;:,.<>?"
    if not any(c in special_chars for c in password):
        errors.append("Password must contain at least one special character")

    return errors

# Test the validator
password = "MyPass123!"
errors = validate_password(password)

if errors:
    print("Password validation failed:")
    for error in errors:
        print(f"  - {error}")
else:
    print("Password is strong!")

# Test various passwords
test_passwords = [
    "weak",           # Too short, no uppercase, no digit, no special
    "WeakPassword",   # No digit, no special
    "WeakPass123",    # No special
    "Strong@Pass1",   # Valid!
]

for pwd in test_passwords:
    errors = validate_password(pwd)
    status = "✓ Valid" if not errors else "✗ Invalid"
    print(f"{pwd:<20} {status}")