Python: Packages

Python programs almost always use code written by others. Reinventing mathematical functions, date handling, or network requests makes no sense — all of this is already available. Python uses packages to share and reuse code.

A package is a directory of Python files organized by topic. The Python standard library contains dozens of such packages, covering everything from mathematics to filesystem access.

Importing a Package

To use code from a package, import it with the import keyword. Let's look at the math package:

import math

print(math.sqrt(16))  # => 4.0
print(math.pi)        # => 3.141592653589793

After import math, everything in the package is available through dot notation: math.sqrt, math.floor, math.pi.

Importing Specific Names

An alternative syntax lets you import only what you need:

from math import sqrt, pi

print(sqrt(25))  # => 5.0
print(pi)        # => 3.141592653589793

Now sqrt and pi are available directly, without the math. prefix. The import math form makes the origin of the function explicit — that helps when reading unfamiliar code. The from math import form is convenient when you need a few specific functions and writing the prefix every time is tedious.

Aliases

The as keyword lets you give an imported name an alias:

from math import sqrt as sq

print(sq(9))  # => 3.0

An alias is useful when a name conflicts with an existing variable or is simply too long.

Standard Library

Python ships with a rich set of built-in packages. A few commonly used ones:

• math — mathematical functions: sqrt, hypot, floor, ceil, pi
• random — random numbers: randint, choice, shuffle
• datetime — working with dates and times

import random

print(random.randint(1, 6))                          # => random number from 1 to 6
print(random.choice(['rock', 'paper', 'scissors']))  # => random element

Third-Party Packages

Beyond the standard library, thousands of packages are created by developers around the world. Install them with pip, Python's package manager:

pip install requests

After installation, imports work the same way as for built-in packages.

Implement the function generate_pin(). It returns a random four-digit PIN code as a string.

Each digit of the PIN is an independent random integer from 0 to 9.

print(generate_pin())  # => e.g. "4823" or "0571"
print(generate_pin())  # => e.g. "1942" or "0037"

Add a return type annotation.

Hint

Generate each of the four digits with random.randint(0, 9) and combine them into a string using an f-string.