pip and PyPI¶

Python has a large ecosystem of third-party libraries.

These libraries are distributed through PyPI and installed using pip.

flowchart LR
    A[Developer]
    A --> B[pip install]
    B --> C[PyPI repository]
    C --> D[Local Python environment]
````

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## 1. What Is PyPI?

PyPI (Python Package Index) is an online repository of Python packages.

It contains thousands of libraries for:

* data science
* web development
* networking
* machine learning
* scientific computing

Examples include:

* `requests`
* `numpy`
* `pandas`
* `flask`

---

## 2. What Is pip?

`pip` is the standard Python package manager.

It downloads and installs packages from PyPI.

Example command:

```bash
pip install requests

3. Installing Packages¶

Example:

pip install numpy

After installation, the module can be imported.

import numpy

4. Listing Installed Packages¶

pip list

This shows all installed packages.

5. Updating Packages¶

pip install --upgrade numpy

6. Virtual Environments (Conceptual Overview)¶

Projects often use virtual environments to isolate dependencies.

flowchart TD
    A[System Python]
    A --> B[Project Environment 1]
    A --> C[Project Environment 2]

Each project can have its own package versions.

7. Worked Example¶

Install the requests library:

pip install requests

Use it in Python:

import requests

response = requests.get("https://example.com")
print(response.status_code)

8. Summary¶

Key ideas:

• PyPI is the central repository of Python packages
• pip installs and manages packages
• third-party libraries expand Python’s capabilities
• virtual environments isolate project dependencies

Package managers make it easy to reuse and distribute Python software.