Home → SCRIPTS → After installing packages in your venv:

PYTHON VIRTUAL ENVIRONMENTS - SETUP & TROUBLESHOOTING

WHY USE VIRTUAL ENVIRONMENTS:
- Isolate project dependencies (each project gets its own packages)
- Avoid version conflicts between projects
- Keep system Python clean
- Make projects portable and reproducible
- Prevent "dependency hell"

SETUP STEPS:

1. Create virtual environment:
   python -m venv project_env

2. Activate virtual environment:
   # Linux/Mac:
   source project_env/bin/activate
   # Windows:
   project_env\Scripts\activate

3. Install project packages:
   pip install package1 package2 package3

4. Save dependencies (optional but recommended):
   pip freeze > requirements.txt

5. Run your script:
   python your_script.py

6. Deactivate when done:
   deactivate

REQUIREMENTS.TXT - DEPENDENCY MANAGEMENT:

What is requirements.txt?
- Text file listing all packages and their versions
- Makes projects reproducible across different machines
- Standard way to share Python project dependencies

Creating requirements.txt:

After installing packages in your venv:

pip freeze > requirements.txt

Or create manually (example content):

PyMuPDF==1.23.5
requests==2.31.0
pandas>=1.5.0

Installing from requirements.txt:

In a new venv or clean environment:

pip install -r requirements.txt

Updating requirements.txt:

After adding new packages:

pip freeze > requirements.txt

Or update specific package:

pip install --upgrade package_name
pip freeze > requirements.txt

Best practices:
- Always include requirements.txt in your project
- Pin versions for reproducibility (==1.2.3)
- Use >= for flexible versions when needed
- Commit requirements.txt to version control

REPRODUCING ENVIRONMENT ON ANOTHER MACHINE:

1. Create and activate venv (steps 1-2 above)
2. Install from requirements:
   pip install -r requirements.txt

TROUBLESHOOTING: Remove packages from global installation

If packages are installed globally and interfering with venv:

1. Make sure you're NOT in any venv:
   deactivate

2. Check what's installed globally:
   pip list | findstr PackageName

3. Uninstall globally:
   pip uninstall PackageName

4. Verify it's gone:
   python -c "import PackageName"
   (Should give "ModuleNotFoundError")

5. Activate venv and install there:
   project_env\Scripts\activate
   pip install PackageName

6. Test isolation:
   # In venv - should work:
   python -c "import PackageName; print('Works in venv')"

deactivate

# Outside venv - should fail:
python -c "import PackageName"

OPTIONAL ALIASES (if python3 command not found):

Linux/Mac (add to ~/.bashrc or ~/.bash_profile):

alias python=python3
alias pip=pip3

Windows (PowerShell profile):

Set-Alias python python3
Set-Alias pip pip3

---

pip install gotcha

Use python3 -m pip install package instead of pip install package

• Ensures you're using the correct Python's pip
• Works when pip isn't in PATH
• Avoids installing to wrong Python version when multiple versions exist
• More reliable and explicit

Last updated: 2025-08-26 20:00 UTC