Hello World

You can find all the code for this chapter here

It is traditional for your first program in a new language to be Hello, World.

• Create a folder wherever you like.
• Create a new file in it called hello.py and put the following code inside it:

def hello():
    print("Hello, world")


hello()

To run it type python hello.py.

How it works

When you write a program in Python you just can define a method and after that just call it.

The def keyword is how you define a function with a name and a body.

Python provide out of the box a function called print that we use to print out to the console.

How to test

How do you test this? It is good to separate your “domain” code from the outside world (side-effects).

The print is a side effect (printing to stdout) and the string we send in is our domain.

So let’s separate these concerns so it’s easier to test

def hello():
    return "Hello, world"


print(hello())

We have created a new function again with def called hello.

Now create a new file called test_hello.py where we are going to write a test for our hello function

from expects import equal, expect

from hello import hello


class TestHello:
    def test_hello(self):
        expect(hello()).to(equal("Hello, world"))