The first program

The common first step in most programming languages is to render the phrase hello, world! to the standard output, so let's do that!

Many compiled languages require creating source files before a single line of code can be written. This isn't strictly the case for Python, which comes with something called a REPL.

REPL: Read, Execute, Print, Loop.

This REPL basically acts as a shell, allowing the user to execute small amounts of code without having to first write an entire source file.

To start, open a terminal on your OS and type python3.

~ ⌚ 12:45:35
$ python3
Python 3.8.10 (default, Jun  2 2021, 10:49:15) 
[GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

This drops you into the Python REPL, where you can type python code and see the results.

As promised, lets say hello to that world!

>>> print("Hello, world!")
Hello, world!
>>>

Unpacking

To better understand what is done, let's unpack the above line of code:

  • print is builtin function, which accepts one argument, and renders that argument it to the standard output.

  • "Hello, world!" is a string literal.

    • A "string" in Computer Science is text, a collection of characters.

  • print("hello world") emits the string `"Hello, World" to the standard output.

More on functions later.