Dictionary Comprehension
Basics
Dictionary Comprehension is a concise way to create dictionaries in Python.
It allows you to generate dictionaries using a single line of code, often making your code more readable and efficient.
# Dictionary comprehension to create a dictionary of squares
squares = {x: x*x for x in range(6)}
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
In the above example, {x: x*x for x in range(6)} is a dictionary comprehension. It iterates over each value x in the range from 0 to 5, squaring x and using it as both the key and the value in the resulting dictionary.
Conditional Dictionary Comprehension
You can also include conditions in dictionary comprehension to filter items based on certain criteria:
# Dictionary comprehension with conditional
even_squares = {x: x*x for x in range(10) if x % 2 == 0}
print(even_squares)
{0: 0, 2: 4, 4: 16, 6: 36, 8: 64}
In this example, only even numbers are included in the resulting dictionary. The condition if x % 2 == 0 filters out odd numbers.
Dictionary Comprehension with Other Iterables
You can use dictionary comprehension with any iterable, not just with ranges:
# Using dictionary comprehension with a list
names = ['Alice', 'Bob', 'Charlie']
name_lengths = {name: len(name) for name in names}
print(name_lengths)
{'Alice': 5, 'Bob': 3, 'Charlie': 7}
In this example, a dictionary is created where each name from the list names is a key, and the length of the name is the corresponding value.
Nested Dictionary Comprehension
You can also nest dictionary comprehensions to create nested dictionaries:
# Using dictionary comprehension with a list
names = ['Alice', 'Bob', 'Charlie']
name_lengths = {name: len(name) for name in names}
print(name_lengths)
{'Alice': 5, 'Bob': 3, 'Charlie': 7}
This example demonstrates how to flatten a matrix into a dictionary. Each element in the flattened matrix is assigned a unique key.
Dictionary comprehension is a powerful tool in Python for creating dictionaries in a compact and expressive manner.