Python Classroom notes 26/Apr/2026

External packages in python

• Python
  • Core Python
  • Standard Library
  • External packages

Lets build a project which will get list of s3 buckets in AWS

• To deal with external packages we need package managers
• Package manager is a software used to manage external packages
• Pacakge managers give us three options
  • Install
  • upgrade
  • remove
• Popular package managers
  • Python:
    • pip
    • uv
  • Nodejs:
    • npm
  • dotnet:
    • nuget

Python – Virtual Environment

How to create a virtual environment using pip

• Create a new folder and cd into it.

python -m venv .venv

• Activate the virtual environment

# windows
.\.venv\Scripts\activate
# linux or mac
source .venv/bin/activate

• Now lets install some packages

pip install numpy

• To list the packages installed we can use pip freeze we store the output of this to a file called as requirements.txt

pip freeze > requirements.txt

• In the version control (git) we store code + requirements.txt

How to create virtual environment and install packages from requirements.txt

• cd into folder where we have code + requirements.txt
• Create the virtual environment and activate

python -m venv .venv
# windows
.\.venv\Scripts\activate
# linux or mac
source .venv/bin/activate

• Now install packages mentioned in requirements.txt

pip install -r requirements.txt

Creating a virtual environment using uv

• Ensure uv is installed
• Create a new folder and cd into it
• initialize uv => this creates a simple project structure

uv init

• To create virtual environment

uv venv
uv sync

• To install packages

uv pip install numpy
uv add numpy

Introduction to unit tests

• Best option is to
  • Developer finding defects.
• Ok OK option is
  • QA/Tester finding defects.
• Worst option is
  • Customer finding defects
• Unit testing is here for that.