Dictionary Comprehensions

Introduction

Basic Dict Comprehension

squares = {x: x**2 for x in range(5)}
print(squares)

With a Condition

evens = {x: x**2 for x in range(10) if x % 2 == 0}
print(evens)

Inverting a Dict

d = {'a': 1, 'b': 2, 'c': 3}
inverted = {v: k for k, v in d.items()}
print(inverted)

From Two Lists

keys = ['name', 'age']
vals = ['Alice', 30]
d = {k: v for k, v in zip(keys, vals)}
print(d)

Transforming Values

d = {'a': 'hello', 'b': 'world'}
result = {k: v.upper() for k, v in d.items()}
print(result)

Nested Dict Comprehension

nested = {i: {j: i*j for j in range(3)} for i in range(3)}
print(nested)

Grouping with Comprehension

words = ['apple', 'art', 'banana', 'blueberry']
grouped = {ch: [w for w in words if w.startswith(ch)] for ch in 'ab'}
print(grouped)

Merging and Overriding

d1 = {'a': 1, 'b': 2}
d2 = {'b': 99, 'c': 3}
merged = {**d1, **d2}
print(merged)

Dict vs defaultdict

from collections import defaultdict
d = defaultdict(list)
for w in ['apple', 'art', 'banana']:
    d[w[0]].append(w)
print(dict(d))

Performance

# Comprehension
squares = {x: x**2 for x in range(1000)}
print(len(squares))

Quick Check

Recap

Keep Going