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Unit 9 • Lesson 2

Working with External Libraries

Overview

Libraries extend Python's core features to handle specialized tasks like math, data analysis, and graphics. You'll learn how to import, install, and explore external libraries such as math, requests, and matplotlib, expanding Python's capabilities for your projects.

Beginner 20–25 min
Next: APIs and Data Retrieval All Units

What You Will Learn in This Lesson

By the end of this lesson, you will know:

  • Built-in vs external libraries: The difference between libraries that come with Python and those you install.
  • Installing libraries: How to use pip to install external libraries.
  • Importing libraries: Different ways to import and use library functions.
  • Popular libraries: Common external libraries and what they do.
  • Library documentation: How to find and use library documentation.

Built-in vs External Libraries

Python comes with many built-in libraries like math, random, and datetime. But for specialized tasks, you'll need external libraries that must be installed first.

Built-in Libraries

Come with Python, work immediately, examples: math, random, datetime, os

External Libraries

Need to install with pip, examples: requests, matplotlib, pandas, numpy

Installing External Libraries

Use pip (Python's package installer) to install external libraries:

Installing a Library
# In your terminal/command prompt:
pip install requests

# Or for Python 3 specifically:
pip3 install requests

pip Command

pip is Python's package manager. It downloads and installs libraries from the Python Package Index (PyPI). Always install libraries in your terminal, not in Python code!

Ways to Import Libraries

There are several ways to import libraries:

Different Import Methods
# 1. Full import
import math
result = math.sqrt(16)

# 2. Import specific functions
from math import sqrt, pi
result = sqrt(16)

# 3. Import with alias
import math as m
result = m.sqrt(16)

# 4. Import everything (not recommended)
from math import *
result = sqrt(16)

Best Practices

  • Use full imports for clarity: import math
  • Use specific imports to avoid namespace pollution: from math import sqrt
  • Use aliases for long names: import matplotlib.pyplot as plt
  • Avoid import * - it makes code harder to read

Finding and Choosing Libraries

How to find the right library for your needs:

1

Search PyPI

Visit pypi.org to search for libraries. PyPI (Python Package Index) is the official repository of Python packages.

2

Read Documentation

Check the library's documentation to understand its features, usage examples, and requirements.

3

Check Popularity

Look at download counts and GitHub stars. Popular libraries are usually well-maintained and have good community support.

4

Read Reviews

Check GitHub issues and discussions to see if the library is actively maintained and has good support.

Installing Specific Versions

You can install specific versions of libraries:

# Install specific version
pip install requests==2.28.0

# Install latest version
pip install requests

# Upgrade existing library
pip install --upgrade requests

Popular External Libraries

Here are some commonly used external libraries and what they do:

Library Purpose Installation
requests Make HTTP requests to APIs and websites pip install requests
matplotlib Create charts and visualizations pip install matplotlib
pandas Data analysis and manipulation pip install pandas
numpy Numerical computing and arrays pip install numpy
beautifulsoup4 Web scraping and HTML parsing pip install beautifulsoup4
flask Build web applications pip install flask
pillow Image processing pip install pillow
selenium Web browser automation pip install selenium

Library Categories

Libraries are often grouped by purpose:

  • Web: requests, flask, django, beautifulsoup4
  • Data Science: pandas, numpy, matplotlib, seaborn
  • Automation: selenium, pyautogui, schedule
  • Utilities: python-dateutil, pytz, colorama

Using Library Documentation

Learning to read library documentation is crucial:

Example: Using requests Library
import requests

# Basic GET request
response = requests.get('https://api.github.com/users/octocat')

# Check status code
if response.status_code == 200:
    data = response.json()
    print(f"Username: {data['login']}")
else:
    print(f"Error: {response.status_code}")

# With error handling
try:
    response = requests.get('https://api.github.com/users/octocat', timeout=5)
    response.raise_for_status()  # Raises exception for bad status codes
    data = response.json()
except requests.exceptions.RequestException as e:
    print(f"Request failed: {e}")

Reading Documentation

When learning a new library:

  1. Start with the "Quick Start" or "Getting Started" section
  2. Look at code examples
  3. Understand the basic concepts
  4. Try the examples yourself
  5. Read the API reference for specific functions

Practice: Using Libraries

Try It Yourself

Try using Python's built-in math library:

Press Run to see output

What happened? You imported the math library and used its functions. External libraries work the same way - install them with pip, then import and use them!

Summary

In this lesson, you learned:

  • Built-in libraries: Come with Python, work immediately
  • External libraries: Need to be installed with pip
  • Import methods: Full import, specific import, aliases
  • Popular libraries: requests, matplotlib, pandas, numpy
  • Best practices: Use clear import statements

Remember

External libraries extend Python's power. Always check library documentation to learn how to use them. The Python community has created libraries for almost everything!

End-of-Lesson Exercises

Think about these questions to reinforce what you've learned:

Exercise 1: Libraries

What is the difference between a built-in library and an external library? Give examples of each.

Exercise 2: Importing

What are the different ways to import a library in Python? When would you use each method?

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