Comprehensions (List, Dictionary, Set)

Intro

  • Python is expressive

  • Clear syntax for everything

  • Sometimes a bit short to the point

  • ⟶ Comprehensions, consequentially

Simplest: List Comprehension

l = []
for i in range(5):
    l.append(i**2)

l

[0, 1, 4, 9, 16]

This is clumsy. Want dedicated sytax!

[i**2 for i in range(5)]

[0, 1, 4, 9, 16]

Even with an included if statement …

[i**2 for i in range(5) if i%2==0]

[0, 4, 16]

%matplotlib inline
import matplotlib.pyplot as plt

x = list(range(5))
y = [i**2 for i in x]
plt.plot(x, y)
plt.show()
../../../../../../_images/topic_3_0.png

Dictionary Comprehension

{i: i**2 for i in range(5)}

{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

{i: i**2 for i in range(5) if i%2==0}

{0: 0, 2: 4, 4: 16}

Set Comprehension

{i for i in range(5)}

{0, 1, 2, 3, 4}

{i for i in range(5) if i%2 == 0}

{0, 2, 4}