Dictionary Comprehensions

Dictionary Comprehensions

Dictionary comprehensions are a concise and efficient way to create dictionaries in Python. They allow you to generate dictionaries by applying an expression to each item in an iterable and specifying key-value pairs within a single line of code. This section covers the basics of dictionary comprehensions and demonstrates their usage.

1. Basic Dictionary Comprehension

The basic syntax of a dictionary comprehension consists of curly braces {} enclosing a key-value expression followed by a for clause.

# Create a dictionary of squares for numbers from 0 to 4
squares = {x: x ** 2 for x in range(5)}

In this example, the expression x ** 2 is applied to each item in the iterable range(5), generating key-value pairs where the key is x and the value is the square of x.

2. Dictionary Comprehension with Condition

You can include an optional condition in a dictionary comprehension to filter items from the source iterable.

# Create a dictionary of even squares for numbers from 0 to 9
even_squares = {x: x ** 2 for x in range(10) if x % 2 == 0}

In this example, the condition x % 2 == 0 filters out odd numbers, resulting in a dictionary of even squares.

3. Transforming Existing Dictionaries

You can use dictionary comprehensions to transform an existing dictionary by applying an expression to its key-value pairs.

# Transform an existing dictionary by squaring the values
original_dict = {'a': 1, 'b': 2, 'c': 3}
squared_values = {k: v ** 2 for k, v in original_dict.items()}

This example creates a new dictionary with the same keys and squared values based on the original dictionary.

4. Benefits of Dictionary Comprehensions

• Conciseness: Dictionary comprehensions provide a compact and readable way to create dictionaries.
• Efficiency: Dictionary comprehensions are optimized for speed and are faster than equivalent for loops.
• Clarity: Dictionary comprehensions express the creation and transformation of dictionaries directly from data, making the code more understandable.

Dictionary comprehensions are a valuable feature in Python for creating dictionaries, transforming existing dictionaries, and filtering items efficiently. They simplify the code and improve readability.