🌱 Junior Track 15 of 15

15. Virtual Environments & Dependency Management

Essential for professional development: `venv`, `source .venv/bin/activate`, `pip install`, `pip freeze > requirements.txt`, `pip install -r`, and modern `pyproject.toml` setup.

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🎓 Junior Python Curriculum — Select Module

1️⃣ Fundamentals 2️⃣ Data Types 3️⃣ Operators 4️⃣ Conditionals 5️⃣ Loops 6️⃣ Collections 7️⃣ Comprehensions 8️⃣ Functions 9️⃣ *args & **kwargs 🔟 Scope & Namespaces 1️⃣1️⃣ OOP 1️⃣2️⃣ Exceptions 1️⃣3️⃣ File Handling 1️⃣4️⃣ Modules & Packages 1️⃣5️⃣ Virtual Environments 1️⃣6️⃣ Standard Library 1️⃣7️⃣ Iterators & Iterables 1️⃣8️⃣ Generators 1️⃣9️⃣ Decorators 2️⃣0️⃣ Context Managers 2️⃣1️⃣ Lambda Functions 2️⃣2️⃣ Functional Programming 2️⃣3️⃣ Type Hints 2️⃣4️⃣ Dataclasses 2️⃣5️⃣ Testing 2️⃣6️⃣ Debugging 2️⃣7️⃣ Logging 2️⃣8️⃣ JSON & Data 2️⃣9️⃣ Regular Expressions 3️⃣0️⃣ Databases

# ==============================================================================
# JUNIOR PYTHON TRACK 15 — VIRTUAL ENVIRONMENTS & PIP COMMANDS
# ==============================================================================

# Step 1: Create Virtual Environment
$ python3 -m venv .venv

# Step 2: Activate Environment
# Linux / macOS (bash & zsh):
$ source .venv/bin/activate

# Windows (Command Prompt):
C:\> .venv\Scripts\activate.bat

# Windows (PowerShell):
PS C:\> .venv\Scripts\Activate.ps1

# Step 3: Install Third-Party Packages
(.venv) $ pip install flask pytest requests

# Step 4: Lock Dependencies into requirements.txt
(.venv) $ pip freeze > requirements.txt

# Step 5: Install Dependencies in a New System / Environment
(.venv) $ pip install -r requirements.txt

# Step 6: Deactivate Virtual Environment
(.venv) $ deactivate

$ python3 -m venv .venv
$ source .venv/bin/activate
(.venv) $ pip install Flask==3.0.2 pytest==8.0.1
Collecting Flask==3.0.2
  Downloading Flask-3.0.2-py3-none-any.whl (101 kB)
Collecting pytest==8.0.1
  Downloading pytest-8.0.1-py3-none-any.whl (335 kB)
Successfully installed Flask-3.0.2 pytest-8.0.1 Werkzeug-3.0.1 Jinja2-3.1.3

(.venv) $ pip freeze > requirements.txt
(.venv) $ cat requirements.txt
Flask==3.0.2
Jinja2==3.1.3
pytest==8.0.1
Werkzeug==3.0.1

(.venv) $ deactivate
$

import sys
import unittest

class TestEnvironmentDetection(unittest.TestCase):
    def test_is_inside_virtualenv(self):
        """Checks if Python is currently executing inside a virtual environment."""
        is_venv = sys.prefix != sys.base_prefix
        print(f"sys.prefix: {sys.prefix}")
        print(f"sys.base_prefix: {sys.base_prefix}")
        print(f"Active in Virtual Environment: {is_venv}")

if __name__ == "__main__":
    unittest.main()

🌱 Junior Track 15 Master Reference

15. Virtual Environments & Dependency Management Reference

1️⃣ Virtual Environment OS Activation Matrix

Operating System	Shell	Activation Command
Linux / macOS	bash / zsh	source .venv/bin/activate
Windows	Command Prompt (cmd)	.venv\Scripts\activate.bat
Windows	PowerShell	.venv\Scripts\Activate.ps1
Any OS	Active shell session	deactivate

2️⃣ Essential `pip` Package Commands

pip install <pkg>: Downloads and installs a package from PyPI.
pip install <pkg>==1.2.3: Installs an exact version.
pip uninstall <pkg>: Removes an installed package.
pip list: Displays all installed packages in active environment.
pip freeze > requirements.txt: Saves exact package versions to a text file.
pip install -r requirements.txt: Installs all listed requirements.

3️⃣ requirements.txt vs Modern `pyproject.toml`

While requirements.txt is standard for locking application deployment dependencies, modern Python projects use pyproject.toml (PEP 621) to specify project metadata, build systems (hatchling, setuptools, poetry), and dependencies in a unified file.

                    # pyproject.toml

                    [project]

                    name = "my_teach_cloud_app"

                    version = "1.0.0"

                    dependencies = [

                        "flask>=3.0.0",

                        "pytest>=8.0.0"

                    ]

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