2.4. Lecture 3: Python 1

Before this class you should:

  • Read Think Python:

    • Preface;

    • Chapter 1: The way of the program;

    • Chapter 2: Variables, expressions and statements; and

    • Chapter 3: Functions

Before next class you should:

  • Read Think Python:

    • Chapter 5: Conditionals and recursion;

    • Chapter 6: Fruitful functions; and

    • Chapter 7: Iteration

Note taker: Zach McMurray

2.4.1. Python Review Class Overview

  • Setting up JupyterHub using the school VPN

  • Working through Python 1a

    • Focus: Operations, variable types/names, and comments

  • Working through Python 1b

    • Focus: Functions

2.4.2. VPN Setup

  1. Visit vpn.uoguelph.ca

  2. Log in using Single Sign-On

  3. Select Split Tunnel

  4. Enable the VPN

2.4.3. JupyterHub

  • Access JupyterHub at engg3130.soe.uoguelph.ca

  • The system syncs with GitHub every 15 minutes

  • JupyterHub contains:

    • Lecture notes

    • Homework details

  • The Public folder is read-only

    • Copy files before starting work

    • Open a new terminal with File -> New -> Terminal

    • Enter:

      cp -r public/homework/homework## work

2.4.4. Python Concepts

Work through the following notebook: Python 1a.ipynb

Note: All students should complete this notebook.

Jupyter Notebook Basics

  • Jupyter notebooks are divided into two types of cells:

    • Markdown – text, links, and math

    • Code – Python code

  • Two modes for cells:

    • Edit Mode

      • Used to modify the contents of a cell

      • Indicated by a green border

      • Press Enter to enter Edit Mode

    • Command Mode

      • Used to run cells or change cell types

      • Indicated by a blue border

      • Press Esc to enter Command Mode

      • Common shortcuts:

        • Shift + Enter: Run cell and move to next

        • Ctrl + Enter: Run cell and stay in place

Basic Python Operations

  • Python supports standard arithmetic operators:

    • Addition: +

    • Subtraction: -

    • Multiplication: *

    • Division: /

    • Exponentiation: **

Common Variable Types

  • int:

    number = 5

  • float:

    number = 5.3

  • str:

    text = "engg3130"

  • bool:

    value = True

Use type() to check a variable’s type.

Variables and Naming Rules

  • Variable names:

    • Must start with a letter or underscore

    • Cannot start with a number

    • Cannot be Python keywords (e.g., if, for, while)

    • Are case-sensitive (value and Value are different)

  • The left-hand side of an assignment must always be a variable name, not an expression.

Strings are a unique type of variable with their own operations.

Example:

course = "ENGG3410"

  • String operations:

    • Concatenation using +:

      "Hello" + " World"

    • Repetition using *:

      "A" * 5

    • Indexing (starting at 0):

      course[0]   # 'E'
course[1]   # 'N'

Interactive Mode vs Script Mode

  • Interactive mode:

    • Evaluates and displays the result of the last line

  • Script mode:

    • Can be called in other cells

    • Does not automatically display results

Comments

  • # is used for comments:

    # This is a comment

Work through the following notebook: Python 1b.ipynb

Note: All students should complete this notebook.

A function is a reusable block of code that performs a specific task.

Why Use Functions?

  • Reduce repeated code

  • Improve readability

  • Break complex problems into smaller pieces

New functions are defined using the def keyword.

Basic Function Structure

Functions have three main parts:

  • Function name

  • Arguments (parameters)

  • Return value (optional)

General syntax:

def function_name(arguments):
    function_body
    return value

A function is executed by calling it using its name followed by parentheses:

function_name(arguments)

Important Ideas for Functions

  • Use import to access additional functions

  • Function headers must end with a colon (:)

  • Code inside a function must be indented

  • Functions can call other functions

  • Variables created inside a function exist only within that function

Types of Functions

  • Fruitful functions

    • Return a value using return

  • Void functions

    • Perform an action but return no value