Python Fundamentals

Last updated on 2026-03-30 | Edit this page

Estimated time: 30 minutes

Overview

Questions

  • How do we process mathematical operations in Python?
  • What happens if we make a mistake?

Objectives

  • Become familiar with mathematical operators and built-in functions.
  • Become more confident using Jupyter notebooks (e.g., writing and running cells).
  • Understand the order of operations.

Simple calculation

Any Python interpreter can be used as a calculator:

Subtraction

PYTHON 

10 - 5 #(subtraction)

OUTPUT 

5

Addition

PYTHON 

10 + 5 #(addition)

OUTPUT 

15

Multiplication

PYTHON 

10 * 5 #(multiplication)

OUTPUT 

50

Division

PYTHON 

10 / 5 #(division)

OUTPUT 

2.0

Exponentiation

PYTHON 

5 ** 2 #(exponentiation)

OUTPUT 

25

Modulus

PYTHON 

10 % 3 #(modulus)

OUTPUT 

1

Note: anything following a ‘#’ is considered a comment. Comments are not read by Python, they are used to help explain the code to other users (and your future self).

Order of operations

Question: Before you enter the next calculation, take a second to consider what answer you would expect.

PYTHON 

6 + 9 / 3

OUTPUT 

9.0

If the answer was not what you were expecting you will need to become clear on order of operations in Python.

Remember BO(DM)(AS) (BIDMAS or PEMDAS)

  • Brackets

  • Orders

  • Division/Multiplication*

  • Addition/Subtraction*

Operators with the same precedence are calculated left to right.

This tells you the order in which mathematical operations will be performed and ensures consistency during evaluation.

To make this concept clearer, try:

PYTHON 

(6 + 9) / 3

OUTPUT 

5.0

Using brackets we have manipulated the order of operations to perform the addition before the division. Be conscious of how you structure your mathematical operations to ensure the desired results but also readability of your code.

So what happens if we do something wrong? I am worried that I might break something!

If we do something wrong, Python will usually show us an error message. Sometimes, more frustratingly, the code will still run but produce unexpected results. This is a normal part of programming and not usually a sign that you have broken anything. So, how do we get help when things don’t work like they should?

Getting Help

We are now going to briefly explore how to find help in Python and introduce our first built-in function. The built-in function we will use is help(), which displays information about Python objects. We will use it to look up another built-in function, print().

Callout

A function is a named piece of code that performs a task. We will look at functions in more detail later in the module. For now, we will use built-in functions (functions included in base Python) to understand how to use them.

Every built-in function has extensive documentation that can also be found online.

PYTHON 

help(print)

OUTPUT 

Help on built-in function print in module builtins:

print(*args, sep=' ', end='\n', file=None, flush=False)
    Prints the values to a stream, or to sys.stdout by default.

    sep
      string inserted between values, default a space.
    end
      string appended after the last value, default a newline.
    file
      a file-like object (stream); defaults to the current sys.stdout.
    flush
      whether to forcibly flush the stream.

This help message (the function’s “docstring”) includes a usage statement, a list of parameters accepted by the function, and their default values if they have them.

It is normal to encounter error messages while programming, whether you are learning for the first time or have been programming for many years. We will discuss error messages in more detail later. For now, let’s explore how people use them to get more help when they are stuck with their Python code.

  • Search the internet: paste the last line of your error message or the word “python” and a short description of what you want to do into your favourite search engine and you will usually find several examples where other people have encountered the same problem and came looking for help.
    • Stack Overflow can be particularly helpful for this: answers to questions are presented as a ranked thread ordered according to how useful other users found them to be.
    • Take care: copying and pasting code written by somebody else is risky unless you understand exactly what it is doing!
  • Ask somebody “in the real world”. If you have a colleague or friend with more expertise in Python than you have, show them the problem you are having and ask them for help.

We will discuss more debugging strategies in greater depth later in the lesson.

Key Points
  • Built-in functions are always available to use (without additional libraries).
  • Use help(thing) to view help for something.
  • You may have seen some error messages already, they provide information about what has gone wrong with your code and where.