Formatting Output in Python

Formatting Output in Python

In Python, formatting output allows you to present data in a readable and structured way. There are several methods for formatting output in Python, which can be useful for making your program’s output more user-friendly. Let’s explore the most common methods.

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1. Using f-strings (Formatted String Literals)

Introduced in Python 3.6, f-strings are the most modern and efficient way to format strings. You can embed expressions inside string literals using curly braces {} and prefix the string with f.

Syntax:

f"string {expression}"

Example:

name = "Pankaj"
age = 25
print(f"My name is {name}, and I am {age} years old.")

Output:

My name is Pankaj, and I am 25 years old.

Advantages of f-strings:

• More readable and concise.

• Allows expressions inside the curly braces, such as calculations or function calls.

Example with expressions:

x = 10
y = 5
print(f"The sum of {x} and {y} is {x + y}.")

Output:

The sum of 10 and 5 is 15.

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2. Using str.format() Method

The str.format() method allows you to format strings by inserting placeholders in the string and passing values to these placeholders.

Syntax:

"string {} {}".format(value1, value2)

Example:

name = "Pankaj"
age = 25
print("My name is {}, and I am {} years old.".format(name, age))

Output:

My name is Pankaj, and I am 25 years old.

Using Indexes and Named Placeholders:

You can also specify the position of the arguments using indexes or name them.

Example with indexes:

print("My name is {0}, and I am {1} years old. {0} is learning Python.".format(name, age))

Output:

My name is Pankaj, and I am 25 years old. Pankaj is learning Python.

Example with named placeholders:

print("My name is {name}, and I am {age} years old.".format(name="Pankaj", age=25))

Output:

My name is Pankaj, and I am 25 years old.

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3. Using % Formatting (Old Style)

This method is an older way to format strings in Python. It is similar to the printf() function in C. Although it is still widely used, it is generally recommended to use f-strings or str.format() for better readability.

Syntax:

"string % (value1, value2)"

Example:

name = "Pankaj"
age = 25
print("My name is %s, and I am %d years old." % (name, age))

Output:

My name is Pankaj, and I am 25 years old.

Common Format Specifiers:

• %s for strings.

• %d for integers.

• %f for floating-point numbers.

Example with floating-point number:

pi = 3.14159
print("The value of pi is approximately %.2f." % pi)

Output:

The value of pi is approximately 3.14.

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4. Controlling Width and Alignment

You can control the width and alignment of the output using formatting techniques.

1. Right-aligning text

Use > to right-align text in a field of a given width.

Example:

name = "Pankaj"
print(f"{name:>10}")  # Right-align with a width of 10

Output:

    Pankaj

2. Left-aligning text

Use < to left-align text in a field of a given width.

Example:

name = "Pankaj"
print(f"{name:<10}")  # Left-align with a width of 10

Output:

Pankaj    

3. Center-aligning text

Use ^ to center-align text in a field of a given width.

Example:

name = "Pankaj"
print(f"{name:^10}")  # Center-align with a width of 10

Output:

  Pankaj  

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5. Formatting Numbers

You can format numbers in Python to control decimal places, add commas for thousands, or represent them in scientific notation.

1. Controlling Decimal Places

Use :.nf to control the number of decimal places, where n is the number of decimal places you want.

Example:

pi = 3.141592653589793
print(f"Value of pi to 3 decimal places: {pi:.3f}")

Output:

Value of pi to 3 decimal places: 3.142

2. Adding Commas for Thousands

Use :, to format numbers with commas as thousands separators.

Example:

number = 1000000
print(f"Number with commas: {number:,}")

Output:

Number with commas: 1,000,000

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6. Combining Multiple Formatting Techniques

You can combine different formatting techniques in a single string.

Example:

name = "Pankaj"
age = 25
pi = 3.14159
print(f"Name: {name:<10} Age: {age:>5} Pi: {pi:.2f}")

Output:

Name: Pankaj     Age:    25 Pi: 3.14

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Conclusion

Python offers several ways to format output, from the modern f-strings to the older % formatting. The most commonly recommended and efficient approach is using f-strings, as they are easier to read and allow for complex expressions. However, depending on your needs, you can also use str.format() or % formatting.

Here’s a quick summary:

• f-strings (recommended): f"Hello, {name}"

• str.format(): "Hello, {}".format(name)

• Old style (%): "Hello, %s" % name

Happy Coding at codeswithpankaj.com! 🚀