Jupyter Notebook

Last updated on 2026-03-04 | Edit this page

Estimated time: 45 minutes

Introduction to Jupyter Notebooks

A Beginner’s Guide for New Data Scientists (Python)

1. What Is a Jupyter Notebook?

A Jupyter Notebook is an interactive computing environment that allows you to combine:

  • Code (Python)
  • Text explanations
  • Mathematical equations
  • Tables and visualizations
  • Results and outputs

All in a single document.

Jupyter Notebooks are especially useful for:

  • Data exploration and analysis
  • Teaching and learning Python
  • Prototyping models
  • Sharing reproducible research

Instead of writing a script and running it all at once, you work in small, executable blocks called cells.

2. Why Data Scientists Use Jupyter Notebooks

Jupyter Notebooks support an iterative workflow:

  1. Write a few lines of code
  2. Run them immediately
  3. Inspect the output
  4. Modify and rerun as needed

Key Advantages

  • Immediate visualization of data
  • Easy experimentation
  • Built-in documentation using Markdown
  • Reproducible analysis
  • Simple sharing with collaborators

3. Getting Started: Opening a Notebook

You can use Jupyter Notebooks in several ways:

  • Through Anaconda Navigator. Install the application, create an account, and launch Jupyter Notebook.

  • Through Google Collab. You would need a google account for this. Then create a new notebook in Drive.

Quick Start in Google Colab (easiest for beginners)

  1. Go to https://colab.research.google.com
  2. Click File → New notebook
  3. You’re ready! No installation needed.

Colab runs in the cloud → you only need a Google account and internet.

Tip: The interface looks almost identical to classic Jupyter.

4. Understanding Cells

A Jupyter Notebook is composed of cells. Each cell performs a specific role.

4.1 Code Cells

  • Used to write and execute Python code
  • Output appears directly below the cell

PYTHON 

x = 10
y = 5
x + y

4.2 Markdown Cells

  • Used for formatted text, headings, lists, and links
  • Supports standard Markdown syntax

4.3 Raw Cells

  • Used infrequently
  • Mostly for advanced formatting or export purposes

Note: This is not too important for our case.

Try it now (in a new notebook):

Code cell 1

PYTHON 

message = "Hello, welcome to Jupyter!"
print(message)

PYTHON 

print(message + " We're going to have fun!")

5. Running Cells

You can execute cells using keyboard shortcuts:

  • Shift + Enter → Run cell and move to next

  • Ctrl + Enter → Run cell and stay in place

  • Alt + Enter → Run cell and insert a new one below

Important: Cells do not need to be run from top to bottom, but execution order matters.

6. The Notebook Kernel

The kernel is the computational engine that runs your code.

For Python notebooks, the kernel:

  • Executes Python code

  • Stores variables in memory

  • Can be restarted or interrupted

Common Kernel Actions

Restart Kernel – Clears all variables

Interrupt Kernel – Stops long-running code

Best practice: Restart the kernel and run all cells before sharing a notebook.

7. Variables and Statefulness – The Most Important Concept

Jupyter remembers variables across cells as long as the kernel is running.

This is very powerful… but also the source of most beginner frustration.

Demo – run these cells one by one

Cell A

PYTHON 

temperature = 20
print("Temperature is", temperature, "°C")

Cell B

PYTHON 

temperature = temperature + 5
print("New temperature:", temperature, "°C")

Cell C

PYTHON 

print("What is the temperature now?", temperature)
Discussion

Challenge

Challenge — Variable Values State

  1. Create 3 new code cells
  2. In cell 1: count = 0
  3. In cell 2: count = count + 1; print(count)
  4. In cell 3: print("Final count:", count)
  5. Run all → should print 1
  6. Now run only cell 2 five times
  7. Run cell 3 again → what happened?

→ You just experienced statefulness live!

8. Working with Data in Jupyter

Most data science workflows start by importing libraries and loading data.

PYTHON 

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt

Loading Data

PYTHON 

df = pd.read_csv("data.csv")
df.head()
Do this Why it helps newcomers
Restart & Run All often Eliminates “ghost variable” bugs
One import block at the top Avoids mysterious NameError
Markdown headers + short comments Makes notebook readable like a story
Small cells (5–15 lines max) Easier to find & fix mistakes

9. Visualization Inside Notebooks

Plots are displayed inline, directly below the code cell.

Example:

PYTHON 

plt.plot([1, 2, 3, 4], [10, 20, 25, 30])
plt.xlabel("X values")
plt.ylabel("Y values")
plt.title("Simple Line Plot")
plt.show()

This makes exploratory analysis fast and interactive.

10. Using Markdown for Documentation

Well-written notebooks tell a story.

Use Markdown cells to:

  • Explain your approach
  • Describe datasets
  • Interpret results
  • Organize sections

Example Notebook Structure:

  1. Title: Exploratory Data Analysis
  2. Dataset Overview
  3. Data Cleaning
  4. Visualization
  5. Key Findings

This improves readability for both technical and non-technical audiences.

11. Common Beginner Mistakes & How to Avoid Them

  1. Running cells out of order
    → Variables get unexpected values
    Fix: Kernel → Restart & Run All often

  2. Forgetting to import libraries in a fresh kernel
    → “NameError: name ‘pd’ is not defined”
    Fix: Put all import statements in the first code cell

  3. One giant code cell with 200 lines
    → Hard to debug, hard to fix mistakes
    Fix: Break logic into small cells (one logical step per cell)

  4. No Markdown explanations
    → Nobody (including future you) understands what you did
    Fix: Add a Markdown cell before/after important code blocks

  5. Sharing notebook without restarting & running all
    → Collaborator sees missing variables or wrong results
    Fix: Always do Kernel → Restart & Run All before sharing/exporting

  6. Assuming outputs are permanent
    → Outputs disappear on kernel restart
    Fix: Rely on code, not on saved output images

12. Best Practices for Newcomers

  • Keep notebooks focused on a single task
  • Use clear section headers
  • Restart and run all cells before finalizing
  • Save notebooks frequently
  • Use descriptive file names
  • Move reusable code into .py files as projects grow

Module Overview

Lesson Overview
Introduction I Introduction to Variable Handling in Jupyter Notebook
Introduction II Introduction to Python Coding in Jupyter Notebook
Introduction III Introduction to Python Plotting in Jupyter Notebook