You run pip install requests, wait for the download, and suddenly your previously working code breaks because of a dependency conflict. Sound familiar?

pip is Python’s package installer, pulling from the massive Python Package Index (PyPI) with over 400,000 packages. Here’s how to use it effectively without breaking things.

The Basics

Install a Package

# Latest version
pip install requests

# Specific version (recommended for production)
pip install requests==2.28.1

# Minimum version
pip install requests>=2.28.0

# Version range
pip install "requests>=2.28.0,<3.0.0"

Upgrade a Package

# Upgrade to latest
pip install --upgrade requests

# See what would be upgraded (dry run)
pip install --upgrade --dry-run requests

Uninstall a Package

pip uninstall requests

# Skip confirmation prompt
pip uninstall -y requests

Investigation & Debugging

What’s Installed?

# List all packages
pip list

# List outdated packages
pip list --outdated

# Show only packages you installed (not dependencies)
pip list --not-required

Package Details

When debugging dependency conflicts or checking licenses:

# Full package info
pip show requests

# Output:
# Name: requests
# Version: 2.28.1
# Summary: Python HTTP for Humans.
# Home-page: https://requests.readthedocs.io
# Author: Kenneth Reitz
# License: Apache 2.0
# Location: /usr/local/lib/python3.9/site-packages
# Requires: charset-normalizer, idna, urllib3, certifi
# Required-by: ...

# See dependency tree
pip show requests --verbose

Working with Requirements

Freeze Current Environment

# Export all installed packages
pip freeze > requirements.txt

# Export only top-level packages (cleaner)
pip list --not-required --format=freeze > requirements.txt

Install from Requirements File

# Install everything
pip install -r requirements.txt

# Upgrade everything
pip install --upgrade -r requirements.txt

Common Workflows

Setting Up a New Project

# Create virtual environment
python -m venv venv
source venv/bin/activate  # On Windows: venv\Scripts\activate

# Install dependencies
pip install -r requirements.txt

# Verify
pip list

Before Deploying

# Check for security vulnerabilities (requires pip-audit)
pip install pip-audit
pip-audit

# Check for outdated packages
pip list --outdated

# Generate clean requirements file
pip freeze > requirements.txt

Fixing Broken Dependencies

# Force reinstall a package and dependencies
pip install --force-reinstall --no-cache-dir requests

# Check for conflicts
pip check

Pro Tips

Always use virtual environments — Never install packages globally:

python -m venv venv
source venv/bin/activate

Pin versions in production — Use exact versions in requirements.txt:

requests==2.28.1  # ✅ Reproducible
requests>=2.28.0  # ❌ May break unexpectedly

Check before upgrading — See what will change:

pip list --outdated
pip install --upgrade --dry-run package-name

References

• 029 Python语法之pip与源码安装
• pip (package manager) - wikipedia