Modules and Imports

Using Python's standard library and third-party packages with import, from...import, and pip.

Overview

A module is simply a Python file (.py) that contains functions, classes, and variables you can reuse in other files. Python ships with an extensive standard library of modules covering math, file I/O, networking, date/time, JSON, regular expressions, and hundreds of other domains all available without installing anything extra. You bring a module into your code with the import statement. There are several forms: - `import math` imports the entire module; access items with `math.sqrt(4)` - `from math import sqrt` imports just sqrt; call it as `sqrt(4)` - `from math import sqrt, pi, floor` import multiple names at once - `import math as m` imports with an alias; `m.sqrt(4)` saves typing For third-party packages (not in the standard library), you install them with pip: `pip install requests`. The virtual environment system (venv) isolates project dependencies so different projects can use different package versions.

Key Points

•`import module` imports a module; access its contents as `module.name`
•`from module import name` imports a specific name into the current namespace
•`import module as alias` lets you use a shorter name (e.g. `import numpy as np`)
•Standard library highlights: math, random, os, sys, datetime, json, pathlib, collections
•Third-party packages installed via pip: `pip install package-name`
•Virtual environments (venv) isolate package versions per project always use them
•Write your own modules: any .py file is a module; import it by its filename (without .py)

Examples

Using the math and random modules

import math
import random

print(math.sqrt(144))      # 12.0
print(math.pi)             # 3.141592653589793
print(math.floor(3.9))     # 3
print(math.ceil(3.1))      # 4
print(math.log(100, 10))   # 2.0

# random module
print(random.random())         # float between 0.0 and 1.0
print(random.randint(1, 10))   # int between 1 and 10 inclusive
names = ["Alice", "Bob", "Carol"]
print(random.choice(names))    # random pick from list
random.shuffle(names)
print(names)                   # shuffled in place

datetime and json modules

from datetime import datetime, timedelta

now = datetime.now()
print(now.strftime("%Y-%m-%d %H:%M"))   # e.g. "2026-01-15 14:30"
tomorrow = now + timedelta(days=1)
print(tomorrow.date())

import json

data = {"name": "Alice", "scores": [95, 82, 91]}
json_str = json.dumps(data)           # Python dict → JSON string
print(json_str)
parsed = json.loads(json_str)         # JSON string → Python dict
print(parsed["name"])                 # Alice

os and pathlib for file system operations

import os
from pathlib import Path

# Current working directory
print(os.getcwd())

# pathlib modern, object-oriented file paths
p = Path(".")
print(list(p.iterdir()))   # list files and folders

home = Path.home()
print(home)                # e.g. /Users/alice or C:\Users\alice

# Join paths safely (works on all OS)
config_path = home / ".config" / "myapp" / "settings.json"
print(config_path)

pathlib (Python 3.4+) is preferred over os.path for file path handling.

Common Mistakes

Naming your file the same as a standard library module (e.g. math.py) your file will shadow the stdlib module
`from module import *` pollutes your namespace with all names only use in exploratory code, never in production
Forgetting to activate a virtual environment before installing packages packages may install globally instead

Note

The Python standard library documentation (docs.python.org/3/library/) is one of the best-written references in programming. Before reaching for a third-party package, check if the stdlib already has what you need.

Modules and Imports

Overview

Key Points

Examples

Common Mistakes

Note

Exercises

Knowledge Check

What is the difference between `import math` and `from math import sqrt`?