String Formatting

String formatting in Python allows you to create well-structured and readable strings by embedding variables or expressions into them. It is a powerful tool for generating dynamic content and making your code more maintainable.

Types of String Formatting

Python offers several ways to format strings:

1. Old-Style Formatting (%):

   • This method uses the % operator to format strings.
   • Example:

     name = "Alice"
     age = 30
     formatted_string = "Name: %s, Age: %d" % (name, age)
     # formatted_string is "Name: Alice, Age: 30"
     

2. str.format() Method:

   • The str.format() method allows you to insert values into placeholders {} in a string.
   • Example:

     name = "Bob"
     age = 25
     formatted_string = "Name: {}, Age: {}".format(name, age)
     # formatted_string is "Name: Bob, Age: 25"
     

   • You can also specify the order of insertion or use named placeholders:

     formatted_string = "Name: {0}, Age: {1}".format(name, age)
     formatted_string_named = "Name: {name}, Age: {age}".format(name="Charlie", age=28)
     # formatted_string_named is "Name: Charlie, Age: 28"
     

3. F-Strings (Formatted String Literals):

   • Introduced in Python 3.6, f-strings provide a concise and readable way to format strings.
   • Example:

     name = "Diana"
     age = 22
     formatted_string = f"Name: {name}, Age: {age}"
     # formatted_string is "Name: Diana, Age: 22"
     

   • F-strings also support expressions:

     formatted_string = f"Next year, {name} will be {age + 1} years old."
     # formatted_string is "Next year, Diana will be 23 years old."
     

Formatting Options

You can control the format of numbers, strings, and other data types with specific options:

• Width and Alignment:

  • Control the width and alignment of text within a formatted string.
  • Example:

    formatted_string = f"{name:<10} | {age:^5} | {'Student':>10}"
    # formatted_string is "Diana      |  22  |    Student"
    

• Number Formatting:

  • Format numbers with specific precision, as decimals, or in scientific notation.
  • Example:

    pi = 3.14159
    formatted_string = f"Pi to 2 decimal places: {pi:.2f}"
    # formatted_string is "Pi to 2 decimal places: 3.14"
    

• Thousands Separator:

  • Add commas or other separators to large numbers.
  • Example:

    large_number = 1000000
    formatted_string = f"{large_number:,}"
    # formatted_string is "1,000,000"
    

• String Formatting with Dictionaries:

  • You can use dictionaries to pass multiple values to format strings.
  • Example:

    data = {"name": "Eve", "age": 27}
    formatted_string = "Name: {name}, Age: {age}".format(**data)
    # formatted_string is "Name: Eve, Age: 27"
    

Escaping Braces

If you need to include braces {} in your string without them being interpreted as placeholders, you can escape them by doubling:

formatted_string = f"{{Escaped braces}} and {{name}}"
# formatted_string is "{Escaped braces} and {name}"