6  Python Basics

This section provides a crash course on basic Python concepts used throughout the course. It is purposefully brief, with additional resources provided at the end.

Tip

Follow along by running these cells in a Jupyter Notebook. Alternatively, run them in the Python Interpreter which can be started with uv run python.

6.1 Using libraries

Most functionality useful for MIKE+ modelling exists in Python packages (e.g. mikeio). Therefore, it’s important to understand how to access functionality in a Python package.

Note

The terms package, library, and module are used interchangeably throughout this course.

6.1.1 Import libraries

Import libraries using the import statement:

import math

Or import specific functionality from a library:

from math import sqrt

6.1.2 Objects

All imports are objects containing some functionality. Objects have members accessible via the dot notation:

math.pi
3.141592653589793

Dot accessors can be chained together, since all members are also objects.

math.pi.is_integer()
False

There are a few common types of objects to be aware of:

  1. Modules: reusable code you can import into your program.
  2. Classes: templates for creating objects with specific properties and behaviors.
  3. Functions / Methods: blocks of code that return a result.
  4. Data: any stored information (e.g. numbers, text).

See the type of an object with:

type(math)
module

See the members of an object with:

dir(math)

Get help for an object:

help(math)

Good libraries have documentation. For example, see the documentation for math.

6.1.3 Using Functions / Methods

Note

This course will use the terms ‘function’ and ‘method’ interchangeably.

Use a function by invoking it with round brackets:

sqrt(25)
5.0

Between the brackets is the function arguments. There’s different ways of specifying arguments. For example, there could be a list of arguments:

math.pow(2, 3)
8.0

6.1.4 Using Classes

Some library functionality is provided via a class that needs to be instantiated before using it.

Below, the Random class is instantiated and assigned to the identifier my_random for reference later on.

from random import Random
my_random = Random()

An instantiation of a class is called an instance, and is also an object whose functionality is accessible with the dot notation:

my_random.random() # returns a random number
0.5594543047379519

6.2 Variables

Store data/objects in named variables by using the assignment operator =.

result = 1 + 1
result
2
Note

A valid name must be used. In general, this means it must start with a letter or underscore.

Variable names can be referenced anywhere after their definition.

result = result * 2
result
4

6.3 Collections

A common need is to have a collection of related data. Perhaps the most common type of collection is a list, which is briefly introduced below.

Create a list with square brackets. Optionally include comma separated elements, otherwise an empty list is created.

my_numbers = [1, 2, 3]
my_numbers
[1, 2, 3]

Append elements to an existing list.

my_numbers.append(4)

Access a specific element by indexing the list with the zero-based index. Zero refers to the first element, one the second, and so on.

my_numbers[0]
1

Access a subset of a list by slicing it. The example below accesses elements with index 0 up to, but excluding, 2.

my_numbers[0:2]
[1, 2]

6.4 Control Logic

Control logic allows the flow of a program to be controlled via boolean conditions.

6.4.1 Conditional statements

Use if statements to execute code only if the specified condition is true.

if 100 > 10:
    print("100 is greater than 10")
100 is greater than 10
Note

The code that the if statement applies to is called a block, which must be indented.

Use else statements after an if statement to execute code only if the condition is untrue.

if 100 < 10:
    print("100 is less than 10")
else:
    print("of course, 100 is not less than 10")
of course, 100 is not less than 10

6.4.2 Loops

A while loop continuously executes a block of code while the specified condition is true.

i = 0
while i < 3:
    print(i)
    i = i + 1
0
1
2

A for loop executes a block of code per element in a specified collection.

for fruit in ["Apple", "Banana", "Orange"]:
    print(fruit)
Apple
Banana
Orange

6.5 Additional resources

Learning Python should be a continuous endeavor through practice. Luckily there’s an abundance of high quality resources online. Here’s a few examples:

Tip

Python is used by a wide variety of domains (e.g. web development). Try to use resources specific for engineering/science applications for a more efficient learning path.

6.6 Example - Using Python’s Interpreter