How to Set PYTHONPATH? Explain Concepts of Namespace, Scope and Packages in python.

skabra1973@gmail.com

4 days ago

How to Set PYTHONPATH? Explain Concepts of Namespace, Scope and Packages in python.

SOLUTION....

Set `PYTHONPATH`

PYTHONPATH is an environment variable that Python uses to add extra directories to sys.path so modules/packages in those directories can be imported.

Quick check (see what Python currently searches):

Temporarily (current shell session)

Linux / macOS (bash / zsh):

Permanently

Linux / macOS: add the export line to ~/.bashrc / ~/.zshrc (or the shell profile you use).
Windows: use System Properties → Environment Variables or run:

Note setx modifies future sessions, not the current.

Alternatives (recommended for development)

Use a virtual environment and pip install -e /path/to/your/package (editable install) so your package is available without relying on PYTHONPATH.
Temporarily at runtime in Python:

Add a .pth file to site-packages containing absolute paths (automatic on interpreter start).

Security & practical notes:

Avoid adding untrusted paths. PYTHONPATH affects imports globally for the session.
Prefer packaging + virtualenv for reproducibility.

How Python finds modules (brief)

When you import x, Python searches sys.path in order. sys.path is initialized roughly as:

The directory containing the running script (or '' for interactive shell) — current working directory first.
Paths listed in PYTHONPATH (if set).
Standard library directories and installed site-packages.

So PYTHONPATH entries are searched before site-packages.

Namespace

A namespace is a mapping from names (identifiers) to objects. Think of it as a dictionary where Python stores associations name -> object.

Common namespaces:

Local namespace: names defined inside a function.
Global (module) namespace: names defined at the top-level of a module.
Built-ins namespace: names provided by Python (e.g., len, int, print).
Class namespace: attributes defined inside a class body.

Namespaces keep names isolated so the same identifier can be reused in different places without conflict.

Scope (LEGB rule)

Scope describes where a name is visible. Python resolves names using the LEGB rule:

Local — inside the current function.
Enclosing — any enclosing function scopes (for nested functions).
Global — module-level names.
Built-in — names in the builtins module.