Python Arrays

Python has no "array" keyword. When tutorials say "array" they almost always mean list. There are arrays in two libraries — useful when you need raw performance or n-dimensional math.

The default: list

nums = [10, 20, 30, 40]
nums.append(50)
print(sum(nums), max(nums), min(nums))

Lists hold values of any type, in any order, and resize automatically. Pick a list unless you have a reason not to.

The standard-library array

array.array is a typed, single-type-only sequence — slightly faster and uses less memory than a list:

from array import array
nums = array('i', [10, 20, 30])   # 'i' = signed int
nums.append(40)
print(nums)

NumPy — the n-dimensional one

For real numeric work — vectors, matrices, science, ML — use NumPy:

# pip install numpy
import numpy as np

a = np.array([1, 2, 3, 4])
print(a * 2)           # element-wise
print(a.mean(), a.sum())

m = np.array([[1, 2], [3, 4]])
print(m @ m)           # matrix multiply

Which to use

Example

# Use list — true "arrays" come from the array or numpy modules.
nums = [10, 20, 30, 40]
nums.append(50)
print(sum(nums), max(nums), min(nums))

Exercise

Test yourself