String Formatting

String formatting is a fundamental skill in Python that allows you to create dynamic and readable strings. Python offers several methods for formatting strings, each with its own strengths and use cases. In this tutorial, we'll cover three primary methods: the `%` operator, the `str.format()` method, and f-strings.

### Using the `%` Operator for String Formatting

The `%` operator is an older method of formatting strings, but it is still widely used in many codebases.


# Define variables
name = "Alice"
age = 25

# Use the % operator for string formatting
formatted_string = "Hello, %s. You are %d years old." % (name, age)
print(formatted_string)
Hello, Alice. You are 25 years old.

In this example, `%s` is a placeholder for a string, and `%d` is a placeholder for an integer. The values in the tuple following the `%` operator replace these placeholders in the string.

### Using the `str.format()` Method

The `str.format()` method is a more modern way of formatting strings and offers greater flexibility and readability.


# Define variables
name = "Bob"
age = 30

# Use the str.format() method for string formatting
formatted_string = "Hello, {}. You are {} years old.".format(name, age)
print(formatted_string)
Hello, Bob. You are 30 years old.

In this snippet, `{}` are placeholders that will be replaced by the arguments passed to the `format()` method.

#### Named Placeholders

You can also use named placeholders with the `str.format()` method.


# Define variables
name = "Charlie"
age = 35

# Use named placeholders with the str.format() method
formatted_string = "Hello, {name}. You are {age} years old.".format(name=name, age=age)
print(formatted_string)
Hello, Charlie. You are 35 years old.

Named placeholders make it clear which values are being substituted, enhancing readability.

### Using F-Strings (Literal String Interpolation)

F-strings, introduced in Python 3.6, are the most modern and efficient way to format strings. F-strings are prefixed with an `f` and use curly braces `{}` to evaluate expressions directly within the string.


# Define variables
name = "Diana"
age = 40

# Use f-strings for string formatting
formatted_string = f"Hello, {name}. You are {age} years old."
print(formatted_string)
Hello, Diana. You are 40 years old.

F-strings are not only concise but also faster than the other methods.

#### Inline Expressions

You can include expressions directly within the curly braces of f-strings.


# Define variables
a = 5
b = 10

# Use expressions within f-strings
formatted_string = f"The sum of {a} and {b} is {a + b}."
print(formatted_string)
The sum of 5 and 10 is 15.

### Formatting Floats and Other Data Types

All three methods allow you to format floats and other data types with specific formatting options.

#### Formatting Floats


# Define a float variable
pi = 3.14159

# Using the % operator
formatted_string = "Pi approximately equals %.2f" % pi
print(formatted_string)

# Using the str.format() method
formatted_string = "Pi approximately equals {:.2f}".format(pi)
print(formatted_string)

# Using f-strings
formatted_string = f"Pi approximately equals {pi:.2f}"
print(formatted_string)
Pi approximately equals 3.14
Pi approximately equals 3.14
Pi approximately equals 3.14

In each method, `:.2f` ensures that the float is formatted to two decimal places.

#### Padding and Alignment

You can control padding and alignment with all three methods.


# Define a list of names
names = ["Alice", "Bob", "Charlie"]

# Using the % operator
for name in names:
    print("%-10s" % name)  # Left-aligned with padding

# Using the str.format() method
for name in names:
    print("{:<10}".format(name))  # Left-aligned with padding

# Using f-strings
for name in names:
    print(f"{name:<10}")  # Left-aligned with padding
Alice     
Bob       
Charlie   
Alice     
Bob       
Charlie   
Alice     
Bob       
Charlie   

In each method, `-10s`, `<10`, and `<10` ensure left-alignment with a total width of 10 characters.

### Combining Multiple Formatting Options

You can combine multiple formatting options to create complex formatted strings.


# Define variables
name = "Emily"
balance = 1234.567

# Using the % operator
formatted_string = "Name: %-10s | Balance: $%8.2f" % (name, balance)
print(formatted_string)

# Using the str.format() method
formatted_string = "Name: {:<10} | Balance: ${:8.2f}".format(name, balance)
print(formatted_string)

# Using f-strings
formatted_string = f"Name: {name:<10} | Balance: ${balance:8.2f}"
print(formatted_string)
Name: Emily      | Balance: $ 1234.57
Name: Emily      | Balance: $ 1234.57
Name: Emily      | Balance: $ 1234.57

In this example, we format the name with left-alignment and padding, and the balance with right-alignment, width, and two decimal places.

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