Python : String Formatting

String formatting in Python allows you to create dynamic strings by inserting variables and values into predefined placeholders within a string. There are multiple ways to format strings in Python, including using the % operator, the str.format() method, and f-strings (introduced in Python 3.6). Here's an overview of each method:

Using % Operator:

The % operator allows you to format strings using placeholders followed by a tuple of values:

name = "Alice" age = 30 formatted_string = "Hello, %s! You are %d years old." % (name, age) print(formatted_string)

In this example:

%s is a placeholder for a string value.
%d is a placeholder for an integer value.
The values (name, age) are passed as a tuple to replace the placeholders.

Using str.format() Method:

The str.format() method allows for more flexibility in formatting strings by using curly braces { } as placeholders:

name = "Bob" age = 25 formatted_string = "Hello, {}! You are {} years old.".format(name, age) print(formatted_string)

In this example, the curly braces { } act as placeholders for the values passed to the format() method.

Using f-Strings (Formatted String Literals):

f-strings provide a concise and readable way to format strings using variables directly within the string:

name = "Charlie" age = 35 formatted_string = f"Hello, {name}! You are {age} years old." print(formatted_string)

In f-strings, the expressions inside curly braces { } are evaluated and replaced with their values at runtime.

Formatting Options:

You can customize the formatting of values using various formatting options, such as specifying the number of decimal places for floats, padding strings with leading zeros, and aligning text within a specified width. Here are some examples:

pi = 3.14159 formatted_pi = f"The value of pi is {pi:.2f}" # Two decimal places print(formatted_pi)

number = 42 formatted_number = f"Number: {number:04}" # Padded with leading zeros print(formatted_number)

text = "Python" formatted_text = f"{'{:<10}'.format(text)}" # Left-aligned within 10 characters print(formatted_text)

Using Named Arguments:

With f-strings and str.format(), you can use named arguments for more clarity and readability:

name = "David" age = 40 formatted_string = f"Hello, {name}! You are {age} years old." print(formatted_string)

Using named arguments
formatted_string = "Hello, {name}! You are {age} years old.".format(name=name, age=age) print(formatted_string)