3.1 Basics

This tutorial covers the basic building blocks of Python: variables, data types, and flow control structures.

Variables

A variable is simply a name you give to a storage location in memory, allowing you to hold and manipulate data. Python is dynamically typed, meaning you don’t have to declare the variable type beforehand; it’s determined automatically when you assign a value.

Use the single equals sign = to assign a value. When naming variables, use descriptive names in “snake_case”, e.g. vehicle_mass, applied_force, etc.

# Input data
age = 40                # [years]
length = 185.3          # [cm]
first_name = "Johan"
is_awesome = True

Data types

These are the fundamental ways Python represents information:

Type	Name	Description	Example
int	Integer	Whole numbers (positive, negative or zero).	`10`, `-5`
float	Floating-point	Numbers with a decimal point.	`3.14`, `99.9`
str	String	A sequence of characters (text), enclosed in quotes	`"Hello"`, `'Python'`
bool	Boolean	Represents truth values, either `True` or `False`	`True`, `False`

To check the data type of a specific variable, use the typeof() function.

typeof(first_name)

The above command will return ‘str’, indicating that the variable first_name is a String.

Flow control

Flow control structures determine the order in which your code executes. They allow your program to make decisions and repeat actions.

Conditional statements

Conditional statements execute different blocks of code based on whether a condition is True or False.

Keyword	Purpose
if	Executes code if the condition is `True`.
elif	(Else if) Checks a new condition if the previous `if`/ `elif` conditions were `False`.
else	Executes code if all preceding conditions were `False`

Note that Python uses indentation (usually four spaces) to define code blocks.

score = 85

if score >= 90:
    print("Grade: 5")
elif score >= 80:
    print("Grade: 4")
else:
    print("Grade: 3 or lower")

Loops

Loops are used to execute a block of code multiple times.

The for loop is used for iterating over a sequence (like a list, string or range of numbers).

for i in range(3): # range(3) returns the numbers 0, 1, 2
    print(i) # outputs: 0, 1 and 2

The while loop executes a block of code as long as its specified condition remains True.

counter = 0

while counter < 3:
    print(counter) # outputs: 0, 1 and 2
    counter += 1 # same thing as counter = counter + 1

Be careful not to create infinite loops, ex. by forgetting to update the counter!