Useful information for beginners
=================================

.. tip::

    If you already know how to run Python programs from a terminal/command line,
    and know what is meant by a "REPL", you should go directly to the
    next page.


The information in this page is not intended to take the place of a
complete introduction for beginners.


What is a REPL?
---------------

A REPL (Read-Eval-Print Loop) is an interactive mode where
we are invited to type in some Python code after
**prompt** (most often written as ``>>>``). Python reads
this code, interprets what it means, and might "print" (show) some
result before showing another prompt waiting for us to enter
more code.

Other words sometimes used instead of the REPL acronym are
"console", "shell", and "interpreter".

.. image:: images/python_terminal.png
   :scale: 50 %
   :alt: Python runing in a terminal

In the image shown above, I have started a python interpreter
using the command ``python``, and entered the code
``print('Hello world!')`` at the prompt.

The ``python`` command refers to whatever you need to type to invoke your
favourite Python interpreter in a terminal on your computer.
It could be ``python``, ``python3``, ``py -3.8``, etc.


How to run a Python program
----------------------------

Instead of using an interpreter to type code when prompted
by Python, you can use an editor, save your program in
a file (named ``hello.py`` in my example) and run
it in a terminal by using the command
``python hello.py``.

.. image:: images/python_terminal2.png
   :scale: 50 %
   :alt: Python runing in a terminal

Another option is to use a program like IDLE which includes
both an editor and a python interpreter.

.. image:: images/python_idle.png
   :scale: 50 %
   :alt: Python runing in IDLE

There exists many other editors designed to be used
by Python programmers.
For example, some of you might be familiar with Mu:

.. image:: images/beginner_mu.png
   :scale: 50 %
   :alt: Python runing in Mu

Summary
-------

You can run Python programs by typing ``python ...`` or ``python3 ...``
in a terminal or by using and editor with a built-in menu
for running Python programs.

In the early part of this documentation, the examples I will use
will be mostly done using ``python ...`` in a Windows terminal.
Even if this is not the way that you normally run Python programs,
it would be most helpful if you tried to follow along by doing
something similar to what I show.