Installing Python, pip & Virtual Environments

Overview

Installing Python is easy; managing it is where beginners get burned. Two rules professionals follow from day one: (1) never install project packages globally — every project gets its own virtual environment, so Project A needing requests 2.31 and Project B needing 2.28 never fight; (2) pin your dependencies in a requirements.txt so any laptop (or server) can recreate the exact setup. This is Python's equivalent of Maven/Gradle dependency management in Java — simpler, but only if you build the venv habit early.

venv + pip — the Professional Workflow

# Create and activate a virtual environment
python -m venv .venv

# Windows:
.venv\Scripts\activate
# macOS/Linux:
source .venv/bin/activate

# Install packages INSIDE the venv
pip install fastapi uvicorn requests

# Save exact versions for teammates/servers
pip freeze > requirements.txt

# On another machine — recreate everything
pip install -r requirements.txt

# Leave the environment
deactivate

Checking Your Setup

python --version        # Python 3.12.x
pip --version           # note the path — should point inside .venv

# Inside Python — quick sanity check
>>> import sys
>>> sys.executable      # full path of the running interpreter
'.../.venv/Scripts/python.exe'
>>> sys.version_info
sys.version_info(major=3, minor=12, ...)

Key Points to Remember

• 1One project = one venv. Always. Activate before installing anything
• 2requirements.txt (pip freeze) makes environments reproducible — commit it, never commit .venv
• 3pip installs from PyPI; pip install -U upgrades; pip uninstall removes
• 4"ModuleNotFoundError but I installed it" almost always means wrong interpreter/venv active