PYTHONPATH Global Setup — Windows, macOS & Linux

Set PYTHONPATH once so Python can import your own packages (bankkit, arithops, etc.) from any project folder without sys.path.append().

Use the playground and quiz to confirm how sys.path is built.

What you will learn

• Set PYTHONPATH permanently on Windows
• Configure it on macOS Intel and Apple Silicon
• Configure it on Linux
• Verify that Python can find your packages
• Understand PYTHONPATH vs sys.path.append()

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Platform overview

Python builds sys.path from:

1. The script's directory
2. Standard library paths
3. Directories listed in PYTHONPATH
4. Site-packages (pip installs)

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Before setting PYTHONPATH

Assume this folder structure:

Important: set the path to the parent folder (packages/), not the bankkit/ folder.

✅ Correct	❌ Wrong
/Users/you/dev/packages	/Users/you/dev/packages/bankkit
D:\\dev\\packages	D:\\dev\\packages\\bankkit

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Windows setup (permanent)

Step 1 — Open Environment Variables

Press Win + R, type sysdm.cpl, and press Enter.

Step 2 — Create PYTHONPATH

Under User variables, click New.

Field	Value
Variable name	PYTHONPATH
Variable value	D:\\dev\\packages

Step 3 — Restart terminal

Close and reopen CMD, PowerShell, or VS Code.

Step 4 — Verify

echo $env:PYTHONPATH
python -c "import sys; print(sys.path)"
python -c "import bankkit.bankinfo as bi; print(bi.BNAME)"

Multiple folders (Windows): separate with semicolon ;

D:\dev\packages;D:\shared\libs

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macOS (Intel & Apple Silicon)

Both Intel and M-series (Apple Silicon) Macs use the same method — only the path string and Python install location may differ.

Step 1 — Open Terminal

Step 2 — Edit .zshrc

nano ~/.zshrc

Add this line:

export PYTHONPATH="/Users/you/dev/packages"

Step 3 — Save and reload

source ~/.zshrc

Step 4 — Verify

echo $PYTHONPATH
python3 -c "import bankkit.bankinfo as bi; print(bi.BNAME)"

Apple Silicon tip: use the same python3 in Terminal and VS Code (often /opt/homebrew/bin/python3).

Intel Mac still on bash? put the same export in ~/.bash_profile.

Multiple folders (macOS / Linux): separate with colon :

export PYTHONPATH="/Users/you/dev/packages:/Users/you/shared/libs"

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Linux setup

Step 1 — Edit .bashrc

nano ~/.bashrc

Add:

export PYTHONPATH="/home/you/dev/packages"

Step 2 — Reload

source ~/.bashrc

Step 3 — Verify

echo $PYTHONPATH
python3 -c "import bankkit.bankinfo as bi; print(bi.BNAME)"

System-wide (all users): add to /etc/environment, then log out and back in.

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How Python finds your package

When Python starts, it automatically adds the PYTHONPATH directory into sys.path. Then this works from any folder:

import bankkit.bankinfo as bi
from bankkit.arithops import sumop

print(bi.BNAME)
sumop(10, 20)

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Super example — end to end

1. Create the package (/home/you/dev/packages/bankkit/):

packages/
    bankkit/
        __init__.py
        bankinfo.py
        arithops.py

2. Set PYTHONPATH to /home/you/dev/packages using the steps above for your OS.

3. Run from anywhere:

# ~/Desktop/demo/main.py — no sys.path.append!
import bankkit.bankinfo as bi
from bankkit.arithops import sumop

print(bi.BNAME)
sumop(100, 250)

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Verify inside VS Code

After setting PYTHONPATH, restart VS Code so the IDE inherits the environment variable.

import sys
import bankkit.bankinfo as bi

print("Bank:", bi.BNAME)
print("First search path:", sys.path[0])

If PYTHONPATH is configured correctly, the import succeeds without any sys.path.append().

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sys.path.append vs PYTHONPATH

Feature	sys.path.append()	PYTHONPATH
Scope	One script	Entire machine
Permanent	No	Yes
Written in	Python code	OS environment
Best for	Testing and notebooks	Real projects
Need in every script?	Yes	No

Use sys.path.append() (temporary)

import sys
sys.path.append("/Users/you/dev/packages")
import bankkit.bankinfo

Use PYTHONPATH (recommended)

# No extra path code needed
import bankkit.bankinfo
import bankkit.arithops

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Interview cheat sheet

Question	Answer
What is PYTHONPATH?	Environment variable that adds directories to Python's module search path
What path should you set?	The parent folder containing your package
Windows separator	; between multiple paths
macOS/Linux separator	: between multiple paths
Temporary alternative	sys.path.append()
Apple Silicon vs Intel?	Same export PYTHONPATH=... — path differs per user

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Module 14 — complete journey

1. Modules overview
2. Custom modules
3. import — 4 syntaxes
4. from … import — 3 syntaxes
5. importlib.reload
6. Multi-module project
7. Packages overview
8. Creating packages
9. Reusing packages
10. PYTHONPATH global setup ← you are here

This completes Module 14: Modules & Packages — you can now build reusable modules, organize them into packages, and import them across real-world Python projects.

Key takeaways

• Set PYTHONPATH to the folder containing your package folders
• Windows: sysdm.cpl → Environment Variables → New PYTHONPATH
• macOS (Intel + Apple Silicon): export PYTHONPATH=... in ~/.zshrc
• Linux: export PYTHONPATH=... in ~/.bashrc
• Always restart the terminal / VS Code and verify with echo $PYTHONPATH and a test import