venv and pip

Virtual Environments & pip: Your Python Toolbox

The Story of the Messy Toybox

Imagine you have ONE big toybox at home. Every toy you get goes into this same box.

One day, you’re building a LEGO castle that needs special blue bricks from Set A. But your friend gave you a different LEGO set (Set B) that also has blue bricks—but they’re a DIFFERENT SIZE!

Now your castle is broken because the wrong bricks got mixed in! 😱

This is exactly what happens in Python without virtual environments.

Your computer has ONE place for all Python packages. If two projects need DIFFERENT versions of the same package… CHAOS!

The Solution: Separate Toyboxes!

What if each project had its OWN toybox?

• Castle project → Castle toybox (with the RIGHT blue bricks)
• Spaceship project → Spaceship toybox (with rocket parts)

Virtual environments are separate toyboxes for each Python project!

🏗️ Creating Virtual Environments

Think of this as building a new empty toybox for your project.

The Magic Command

python -m venv myproject_env

Let’s break this down like building blocks:

• python → Hey Python, listen up!
• -m venv → Use your “make environment” tool
• myproject_env → Name your toybox anything you want!

What Just Happened?

Python created a NEW folder called myproject_env with:

myproject_env/
├── bin/           (or Scripts/ on Windows)
├── include/
├── lib/
└── pyvenv.cfg

This folder IS your toybox. It has its own Python and space for packages!

Real Example

Let’s say you’re making a weather app:

python -m venv weather_app_env

Now you have a dedicated toybox just for your weather app!

🔌 Activating Environments

Building the toybox isn’t enough. You need to open it and step inside!

Think of it Like This:

Before activation: You’re standing OUTSIDE the toybox, using your old toys.

After activation: You’re INSIDE the toybox, using only those specific toys!

The Activation Commands

On Mac/Linux (Terminal):

source myproject_env/bin/activate

On Windows (Command Prompt):

myproject_env\Scripts\activate

On Windows (PowerShell):

myproject_env\Scripts\Activate.ps1

How Do You Know It Worked?

Your terminal prompt changes! You’ll see:

(myproject_env) $

That (myproject_env) at the start? That’s like a badge saying “You’re inside this toybox now!”

Getting Out (Deactivating)

When you’re done playing:

deactivate

Simple! You step out of the toybox and return to normal.

📦 pip: The Package Manager

pip is like a magical delivery truck. 🚚

You tell it what toy (package) you want, and it:

1. Finds it in the big toy store (PyPI)
2. Delivers it to YOUR toybox
3. Sets it up so it works!

The Name is Fun!

pip = “pip Installs Packages”

(Yes, it’s a joke name that uses itself! 😄)

Basic pip Commands

Install a package:

pip install requests

This says: “Delivery truck, bring me the ‘requests’ package!”

Install a SPECIFIC version:

pip install requests==2.28.0

This says: “I want version 2.28.0 EXACTLY. Not newer, not older!”

See what’s in your toybox:

pip list

Shows ALL packages currently installed.

Get info about a package:

pip show requests

Tells you version, author, and more!

Remove a package:

pip uninstall requests

Bye bye, package!

📋 requirements.txt: Your Shopping List

Imagine you built an AMAZING project with 20 different packages.

Your friend wants to build the same thing. Do they have to remember all 20 packages and their exact versions?

NO WAY!

You give them a shopping list: requirements.txt

What It Looks Like

requests==2.28.0
flask==2.3.2
numpy==1.24.0
pandas==2.0.1

Simple text file. One package per line.

Creating Your Shopping List

After installing all your packages:

pip freeze > requirements.txt

pip freeze = Show me EVERYTHING installed > = Save it to a file requirements.txt = The file name

Using Someone’s Shopping List

You got a project from GitHub with a requirements.txt?

pip install -r requirements.txt

The -r means “read from this file and install EVERYTHING in it!”

Magic! One command installs all 20, 50, or 100 packages! 🎉

🔧 Package Installation: The Full Picture

Let’s put it ALL together with a story!

Story: Sarah’s Weather App

Day 1: Starting Fresh

Sarah wants to build a weather app.

# Step 1: Create her toybox
python -m venv weather_env

# Step 2: Step inside
source weather_env/bin/activate

# Her prompt now shows:
(weather_env) $

Day 2: Adding Packages

She needs packages to fetch weather data.

# Install the requests library
pip install requests

# Install a weather API helper
pip install python-weather

# Check what's installed
pip list

Output:

Package         Version
--------------- -------
requests        2.28.0
python-weather  1.0.3
pip             23.0

Day 3: Sharing with Friends

Her friend Jake wants to work on the project too!

# Sarah creates the shopping list
pip freeze > requirements.txt

Sarah sends Jake the project. Jake does:

# Jake creates his OWN toybox
python -m venv weather_env

# Steps inside
source weather_env/bin/activate

# Installs EVERYTHING from Sarah's list
pip install -r requirements.txt

Now Jake has the EXACT same setup! No version conflicts! 🎊

The Complete Workflow

graph TD
    A["Start New Project"] --> B["Create venv"]
    B --> C["Activate venv"]
    C --> D["Install packages with pip"]
    D --> E["Write your code"]
    E --> F["Save requirements.txt"]
    F --> G["Share project"]
    G --> H["Friend creates venv"]
    H --> I["Friend installs from requirements.txt"]
    I --> J["Everyone has same setup!"]

Quick Reference: The Commands You’ll Use Daily

Why This Matters

Without virtual environments:

• Projects fight over package versions ⚔️
• “It works on my computer!” problems 😫
• Messy, unpredictable setups 🌪️

With virtual environments:

• Each project is isolated and clean ✨
• Share exact setups with teammates 🤝
• Professional, reproducible code 🏆

You Did It! 🎉

You now understand:

• ✅ Virtual environments = Separate toyboxes
• ✅ venv creates them
• ✅ Activation = stepping inside
• ✅ pip = your delivery truck
• ✅ requirements.txt = your shopping list

These tools are used by EVERY Python developer, from beginners to experts at Google and Netflix!

You’re now ready to build Python projects the professional way!