The Easy Way to Create Dictionaries in Python

Dictionary Comprehensions: A Simple and Powerful Tool

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Dictionary comprehensions are a concise and efficient way to create dictionaries in Python. They allow you to create a new dictionary based on an existing iterable, such as a list or another dictionary. Here’s how they work and why you should use them.

Let’s start with a simple example. Suppose you have a list of numbers and you want to create a dictionary that maps each number to its square. The traditional way would be to use a for loop:

numbers = [1, 2, 3, 4, 5]
squared_numbers = {}

for num in numbers:
    squared_numbers[num] = num ** 2

print(squared_numbers)
# Output: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

While this works, it’s a bit verbose. Dictionary comprehensions allow you to do the same thing in a single line:

numbers = [1, 2, 3, 4, 5]
squared_numbers = {num: num ** 2 for num in numbers}

print(squared_numbers)
# Output: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

The syntax is similar to list comprehensions, but with curly braces {} instead of square brackets []. The expression num: num ** 2 defines the key-value pairs in the new dictionary, and for num in numbers is the iterator.