199 lines
3.4 KiB
Markdown
199 lines
3.4 KiB
Markdown
# pip
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`pip` is Python’s **package manager**.
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It’s the tool you use to **install, upgrade, and remove Python libraries** that aren’t included in the standard library.
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Think of it like:
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* `apt` on Debian/Ubuntu
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* `dnf` on Fedora
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* `npm` for JavaScript
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## What does pip do?
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With `pip`, you can:
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1. **Install packages**
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```bash
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pip install requests
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```
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2. **Upgrade packages**
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```bash
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pip install --upgrade requests
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```
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3. **Uninstall packages**
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```bash
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pip uninstall requests
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```
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4. **List installed packages**
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```bash
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pip list
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```
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5. **Install from a requirements file**
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```bash
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pip install -r requirements.txt
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```
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## Where do packages come from?
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By default, pip downloads packages from **PyPI** (Python Package Index):
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* [https://pypi.org](https://pypi.org)
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* Contains **hundreds of thousands** of Python libraries
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* Example packages: `requests`, `numpy`, `flask`, `django`, `pandas`
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## pip vs Python itself
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* **Python** → the programming language + standard library
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* **pip** → installs *extra* libraries written by the community
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Example:
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```python
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import math # standard library (no pip needed)
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import requests # external library (installed via pip)
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```
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## pip and Python versions
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On many systems:
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* `pip` → Python 2 or system default
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* `pip3` → Python 3
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Safer way (recommended):
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```bash
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python3 -m pip install requests
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```
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This ensures pip matches the Python version you’re using.
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## Virtual environments
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`pip` works best with **virtual environments** ([venv](pages/requirement/venv.md)) to avoid breaking system Python:
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```bash
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python3 -m venv venv
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source venv/bin/activate
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pip install flask
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```
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## What is `requirements.txt`?
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`requirements.txt` is a **list of Python packages** (and versions) your project depends on.
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Example:
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```txt
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flask==3.0.0
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requests>=2.31.0
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gunicorn
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```
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## Install dependencies from `requirements.txt`
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### Basic usage
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```bash
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pip install -r requirements.txt
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```
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### Safer (recommended)
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```bash
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python3 -m pip install -r requirements.txt
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```
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This ensures pip matches your Python version.
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## Use with a virtual environment (best practice)
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```bash
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python3 -m venv venv
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source venv/bin/activate
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pip install -r requirements.txt
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```
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After activation, all packages go into `venv/`.
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## Generate `requirements.txt` from current environment
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If you already installed packages:
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```bash
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pip freeze > requirements.txt
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```
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⚠️ This captures **everything** installed in the environment.
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## Common version formats
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```txt
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flask==3.0.0 # exact version (reproducible builds)
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requests>=2.31.0 # minimum version
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numpy~=1.26.0 # compatible release
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django<5.0 # version upper limit
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```
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## Install from multiple requirement files
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```bash
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pip install -r base.txt -r dev.txt
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```
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Useful for:
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* `base.txt` → production
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* `dev.txt` → development tools (pytest, black, etc.)
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## Requirements from Git / local path
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```txt
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git+https://github.com/pallets/flask.git
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-e .
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```
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Then install:
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```bash
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pip install -r requirements.txt
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```
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## Debian / system Python warning (important)
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On Debian-based systems, **don’t install globally** unless you know what you’re doing:
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❌ Bad:
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```bash
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sudo pip install -r requirements.txt
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```
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✅ Good:
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```bash
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python3 -m venv venv
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pip install -r requirements.txt
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```
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## Typical workflow (TL;DR)
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```bash
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python3 -m venv venv
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source venv/bin/activate
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pip install -r requirements.txt
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python app.py
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```
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