String Operations and Formatting

Master string manipulation and formatting in Python.

String Concatenation

Combine strings using +:

first = "Hello"
second = "World"
result = first + " " + second
print(result)  # Output: Hello World

# Multiple concatenations
greeting = "Good" + " " + "morning" + "!"
print(greeting)  # Output: Good morning!

String Repetition

laugh = "Ha" * 3
print(laugh)  # Output: HaHaHa

# Create separators
separator = "=" * 50
print(separator)

String Indexing and Slicing

Access characters and substrings:

text = "Python"

# Positive indexing
print(text[0])   # P
print(text[5])   # n

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

# Slicing [start:end:step]
print(text[0:3])   # Pyt
print(text[2:])    # thon
print(text[:4])    # Pyth
print(text[::2])   # Pto (every 2nd char)
print(text[::-1])  # nohtyP (reverse)

String Methods

Python provides many built-in string methods:

Case Conversion

text = "Hello, World!"

print(text.upper())       # HELLO, WORLD!
print(text.lower())       # hello, world!
print(text.title())       # Hello, World!
print(text.capitalize())  # Hello, world!
print(text.swapcase())    # hELLO, wORLD!

Searching and Checking

text = "Python Programming"

# Find substring
print(text.find("Pro"))      # 7
print(text.find("Java"))     # -1 (not found)

# Count occurrences
print(text.count("o"))       # 2

# Check start/end
print(text.startswith("Py")) # True
print(text.endswith("ing"))  # True

# Check content
print("123".isdigit())       # True
print("abc".isalpha())       # True
print("abc123".isalnum())    # True

Trimming and Splitting

# Remove whitespace
text = "  Hello  "
print(text.strip())   # "Hello"
print(text.lstrip())  # "Hello  "
print(text.rstrip())  # "  Hello"

# Split into list
sentence = "Python is awesome"
words = sentence.split()
print(words)  # ['Python', 'is', 'awesome']

# Split by delimiter
data = "apple,banana,orange"
fruits = data.split(",")
print(fruits)  # ['apple', 'banana', 'orange']

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

Replacing

text = "I love Java"
new_text = text.replace("Java", "Python")
print(new_text)  # "I love Python"

# Replace multiple occurrences
text = "ha ha ha"
new_text = text.replace("ha", "HO")
print(new_text)  # "HO HO HO"

String Formatting

F-Strings (Recommended)

name = "Alice"
age = 25
height = 5.6

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

# Multiple variables
print(f"{name} is {age} years old")

# Expressions
print(f"Next year, {name} will be {age + 1}")

# Formatting numbers
pi = 3.14159
print(f"Pi is approximately {pi:.2f}")  # 3.14

price = 19.5
print(f"Price: ${price:.2f}")  # Price: $19.50

format() Method

name = "Bob"
age = 30

# Positional arguments
print("My name is {} and I am {}".format(name, age))

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

# Formatting
print("Pi: {:.3f}".format(3.14159))  # Pi: 3.142

# Currency formatting
print("Price: ${:.2f}".format(19.99))  # Price: $19.99

% Formatting (Old Style)

name = "Charlie"
age = 35

print("My name is %s and I am %d" % (name, age))
print("Price: $%.2f" % 19.99)

Escape Characters

Special characters in strings:

# Newline
print("Line 1\nLine 2")

# Tab
print("Column1\tColumn2")

# Backslash
print("C:\\Users\\Documents")

# Quotes
print("She said, \"Hello!\"")
print('It\'s a beautiful day')

# Raw strings (ignore escapes)
print(r"C:\Users\Documents")  # C:\Users\Documents

Practical Examples

Example 1: Format User Information

first_name = "John"
last_name = "Doe"
age = 28
email = "john.doe@email.com"

print("=" * 40)
print(f"Name: {first_name} {last_name}")
print(f"Age: {age}")
print(f"Email: {email}")
print("=" * 40)

Example 2: Create a Receipt

item1 = "Coffee"
price1 = 4.50

item2 = "Sandwich"
price2 = 7.25

total = price1 + price2

print("RECEIPT")
print("-" * 30)
print(f"{item1:<20} ${price1:>6.2f}")
print(f"{item2:<20} ${price2:>6.2f}")
print("-" * 30)
print(f"{'TOTAL':<20} ${total:>6.2f}")

Example 3: Username Generator

first_name = "Alice"
last_name = "Smith"
year = 2025

# Create username
username = (first_name[:3] + last_name[:3] + str(year)[-2:]).lower()
print(f"Generated username: {username}")  # alismi25

Common String Operations Summary

Practice Exercises

1. Create a program that formats personal information nicely
2. Build a string that reverses the order of words in a sentence
3. Extract domain from email addresses
4. Create formatted receipts or invoices
5. Practice all string methods with different examples

Module Complete! Move on to Module 2: Control Flow & Logic