Numbers

You can find all the code for this chapter here

Numbers in Python work as you would expect. There are two main types:

• int for integer numbers.
• float for decimal numbers.

Note: There is also the complex type, but we won’t be covering that here.

Operators

Python is actualy quite normal regarding numbers, you can apply them the typical operations like:

• + for addition.
• - for subtraction.
• * for multiplication.
• / for division.
• // for integer division.
• % for modulo.
• ** for exponentiation.

So let’s write an add function to try things out and play a little bit with them!.

Create a test file called test_adder.py and write this code.

Write the test first

from expects import equal, expect


class TestAdder:
    def test_add(self):
        result = add(1, 2)

        expect(result).to(equal(3))

Try and run the test

================= short test summary info ================= 
FAILED test_adder.py::TestAdder::test_add
NameError: name 'add' is not defined
================= 1 failed in 0.02s ============

Write the minimal amount of code to make it run

Write enough code to satisfy the compiler and that’s all - remember we want to check that our tests fail for the correct reason.

def add(a, b):
    pass

If we run the test again we should see a different error.

E       expected: None to be 2
================= short test summary info ================= 
FAILED test_adder.py::TestAdder::test_add
AssertionError: 
================= 1 failed in 0.02s ============

Write enough code to make it pass

In the strictest sense of TDD we should now write the minimal amount of code to make the test pass. A pedantic programmer may do this

def add(a, b):
    return 3

If we run the test again it should pass.

========================= 1 passed in 0.01s ========================= 

Refactor

We could write another test, with some different numbers to force that test to fail but that feels.

Or we can parametrize the test to make it more flexible.

import pytest
from adder import add
from expects import equal, expect


class TestAdder:
    @pytest.mark.parametrize(
        "x,y,expected",
        [
            (1, 2, 3),
            (2, 2, 4),
            (10, 100, 110),
        ],
    )
    def test_add(self, x, y, expected):
        result = add(x, y)

        expect(result).to(equal(expected))

If you now run the tests you should see them fail.

================= short test summary info ================= 
...
E       expected: 4 to be 3
FAILED test_adder.py::TestAdder::test_add
AssertionError: 

...

E       expected: 110 to be 3
FAILED test_adder.py::TestAdder::test_add
AssertionError: 
...
================= 1 failed in 0.02s ============

Let’s fix it!

def add(a, b):
    return a + b

========================= 3 passed in 0.01s ========================= 

Wrapping up

What we have covered:

• More practice of the TDD workflow.
• Integers, Decimals, addition.
• Principal numbers operations in Python.

Your turn

A great way to learn is doing, so here are some ideas to keep practicing:

• Write a test for the other operations like subtraction, multiplication, division, etc.