Python Core | VoidX Academy

4. Python Strings

Core Concept

Python Strings

Strings are one of the most fundamental data types in Python. A string is a sequence of characters — letters, numbers, spaces, punctuation — enclosed in quotes. Any time you work with text in Python, you are working with strings.

Python strings are immutable, which means once a string is created, it cannot be changed in place. Instead, string operations always create and return a new string. Understanding this behavior is critical to writing correct Python code.

Creating Strings

Strings can be created using single quotes, double quotes, or triple quotes. Triple-quoted strings are especially powerful because they can span multiple lines.

a = 'Hello'              # Single quotes
b = "World"              # Double quotes
c = """This string
spans multiple
lines."""  # Triple quotes

print(a)
print(b)
print(c)

OutputHello World This string spans multiple lines.

String Length

The built-in len() function returns the total number of characters in a string — including spaces, punctuation, and special characters. Every character counts.

text = "Hello, World!"
print(len(text))

Output13

The string "Hello, World!" has 13 characters: 5 + 1 (comma) + 1 (space) + 5 + 1 (exclamation) = 13.

String Indexing

Every character in a string has a position called an index. Python uses zero-based indexing, meaning the first character is at index 0, not 1. You access individual characters using square brackets.

name = "Python"

print(name[0])   # First character
print(name[1])   # Second character
print(name[-1])  # Last character (negative indexing)
print(name[-2])  # Second-to-last character

OutputP y n o

Negative indexing lets you count from the end of the string. -1 is always the last character, -2 is second-to-last, and so on.

String Slicing

Slicing extracts a portion of a string. The syntax is string[start:end], where start is inclusive and end is exclusive (the character at end is not included).

text = "Hello, World!"

print(text[0:5])   # Characters at index 0, 1, 2, 3, 4
print(text[7:12])  # Characters at index 7, 8, 9, 10, 11
print(text[:5])    # From the start up to (not including) index 5
print(text[7:])    # From index 7 to the very end
print(text[-6:-1]) # Using negative indices

OutputHello World Hello World! World

String Methods

Python strings come with a rich library of built-in methods — functions you call on a string object using dot notation. Each method returns a new string without modifying the original.

text = "  Hello, World!  "

print(text.upper())       # ALL UPPERCASE
print(text.lower())       # all lowercase
print(text.strip())       # Remove leading and trailing whitespace
print(text.replace("World", "Python"))  # Replace a word
print(text.split(","))   # Split into a list at commas

Output HELLO, WORLD! hello, world! Hello, World! Hello, Python! [' Hello', ' World! ']

String Concatenation

Concatenation means joining strings together. In Python, you use the + operator to concatenate strings. You can also use the * operator to repeat a string multiple times.

first = "Hello"
second = "World"

result = first + ", " + second + "!"
print(result)

# Repeating a string
line = "-" * 20
print(line)

OutputHello, World! --------------------

F-Strings (String Formatting)

F-strings (formatted string literals) are the modern, preferred way to embed variables directly inside strings. Place the letter f before the opening quote, then wrap any variable or expression in curly braces { } inside the string.

name = "Alice"
age = 25
height = 5.7

message = f"My name is {name}. I am {age} years old and {height}m tall."
print(message)

# You can also put expressions directly inside
print(f"In 10 years, Alice will be {age + 10} years old.")

OutputMy name is Alice. I am 25 years old and 5.7m tall. In 10 years, Alice will be 35 years old.

💡Best Practice: Always use f-strings for string formatting in modern Python (3.6+). They are faster than .format(), more readable than % formatting, and allow full Python expressions inside the curly braces.

Checking String Content

Python provides two powerful keywords — in and not in — to check whether a substring exists inside a larger string. This returns a boolean: True or False.

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

print("fox" in text)
print("cat" in text)
print("cat" not in text)

OutputTrue False True

4. Python Strings

Core Concept

Python Strings

Creating Strings

Strings can be created using single quotes, double quotes, or triple quotes. Triple-quoted strings are especially powerful because they can span multiple lines.

a = 'Hello'              # Single quotes
b = "World"              # Double quotes
c = """This string
spans multiple
lines."""  # Triple quotes

print(a)
print(b)
print(c)

OutputHello World This string spans multiple lines.

String Length

The built-in len() function returns the total number of characters in a string — including spaces, punctuation, and special characters. Every character counts.

text = "Hello, World!"
print(len(text))

Output13

The string "Hello, World!" has 13 characters: 5 + 1 (comma) + 1 (space) + 5 + 1 (exclamation) = 13.

String Indexing

name = "Python"

print(name[0])   # First character
print(name[1])   # Second character
print(name[-1])  # Last character (negative indexing)
print(name[-2])  # Second-to-last character

OutputP y n o

Negative indexing lets you count from the end of the string. -1 is always the last character, -2 is second-to-last, and so on.

String Slicing

Slicing extracts a portion of a string. The syntax is string[start:end], where start is inclusive and end is exclusive (the character at end is not included).

text = "Hello, World!"

print(text[0:5])   # Characters at index 0, 1, 2, 3, 4
print(text[7:12])  # Characters at index 7, 8, 9, 10, 11
print(text[:5])    # From the start up to (not including) index 5
print(text[7:])    # From index 7 to the very end
print(text[-6:-1]) # Using negative indices

OutputHello World Hello World! World

String Methods

Python strings come with a rich library of built-in methods — functions you call on a string object using dot notation. Each method returns a new string without modifying the original.

text = "  Hello, World!  "

print(text.upper())       # ALL UPPERCASE
print(text.lower())       # all lowercase
print(text.strip())       # Remove leading and trailing whitespace
print(text.replace("World", "Python"))  # Replace a word
print(text.split(","))   # Split into a list at commas

Output HELLO, WORLD! hello, world! Hello, World! Hello, Python! [' Hello', ' World! ']

String Concatenation

Concatenation means joining strings together. In Python, you use the + operator to concatenate strings. You can also use the * operator to repeat a string multiple times.

first = "Hello"
second = "World"

result = first + ", " + second + "!"
print(result)

# Repeating a string
line = "-" * 20
print(line)

OutputHello, World! --------------------

F-Strings (String Formatting)

name = "Alice"
age = 25
height = 5.7

message = f"My name is {name}. I am {age} years old and {height}m tall."
print(message)

# You can also put expressions directly inside
print(f"In 10 years, Alice will be {age + 10} years old.")

OutputMy name is Alice. I am 25 years old and 5.7m tall. In 10 years, Alice will be 35 years old.

Checking String Content

Python provides two powerful keywords — in and not in — to check whether a substring exists inside a larger string. This returns a boolean: True or False.

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

print("fox" in text)
print("cat" in text)
print("cat" not in text)

OutputTrue False True

4. Python Strings

Python Strings

Creating Strings

String Length

String Indexing

String Slicing

String Methods

String Concatenation

F-Strings (String Formatting)

Checking String Content

Knowledge Check

4. Python Strings

Python Strings

Creating Strings

String Length

String Indexing

String Slicing

String Methods

String Concatenation

F-Strings (String Formatting)

Checking String Content

Knowledge Check