Python pip & Packages
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What is pip?
pip is Python's package installer, letting you pull third-party code from the Python Package Index (PyPI) with a single command like 'pip install requests' instead of manually downloading and configuring a library yourself.
Example: What is pip?
# pip install requests
print("pip installs packages from PyPI")The requirements.txt File
A requirements.txt file pins the exact packages (and often exact versions) a project depends on, so anyone else can recreate your environment with 'pip install -r requirements.txt' instead of guessing which libraries and versions you used.
Example: The requirements.txt File
# requirements.txt would contain:
# requests==2.31.0
# Install with: pip install -r requirements.txt
print("requirements.txt pins project dependencies")Virtual Environments
A virtual environment creates an isolated Python installation just for one project, so installing a package there doesn't affect (or conflict with) packages installed for other projects on the same machine -- this is what makes reproducible, per-project dependencies possible.
Example: Virtual Environments
# python -m venv venv
# source venv/bin/activate
print("Virtual environments isolate per-project dependencies")Querying Installed Packages
You can inspect where pip actually installs packages by checking a project's site-packages directory, which is useful for debugging 'why isn't Python finding my installed library' issues -- often the answer is that pip installed into a different Python environment than the one running your script.
Example: Querying Installed Packages
import sys
print(sys.prefix) # shows which Python environment is activeBest Practices
Wrapping a third-party import in try/except ImportError lets your program fail with a clear, actionable message ('please install requests') instead of a confusing traceback, which matters most for optional dependencies that not every user of your script will need.
Example: Best Practices
try:
import requests
except ImportError:
print("please install requests")Chapter Quiz — Complete all 6 topics to unlock
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