And to start with Python, first start the Python shell.
So if you don't know how to start it, please go back to the introduction section
where you can see the lesson on how to install
Python on Windows, on Linux, and on Mac OS.
And then come back here for the explanations.
So this is the Python shell, and the first thing you
can see here is the Python version you have here.
So I have version 3, Python 3.9,
but just the important thing is that you have Python 3, okay?
And then you are going to see here three brackets, three angle brackets,
and that's where you are going to type some Python instructions.
So we will see later that you can create complete files with lots of lines of code,
which are basically all instructions that are going to be executed.
And with the Python shell instead, you don't write a complete file,
you just write one instruction at a time, and when you press enter,
the instruction is going to be executed, and in
addition to that, the result of the instruction
will also be evaluated and printed directly on the shell.
So let's just type anything.
Let's just type number 3.
I am going to press enter, and you can see now I have 3 here.
So that was the instruction, which is just a number for now,
so it doesn't do anything, but you can see
we have the instruction, which is evaluated.
So of course, 3 is evaluated to 3, and it's printed here.
I can also do "Hello World" like this.
So use double quotes for now.
Okay, "Hello World", I press enter, and you can see "Hello World".
So here you have your first "Hello World" program in Python.
And in this section, we are going to continue with
this Python shell to discover variables, et cetera.
And so you can just type literal value like this,
and you can also, for example, use Python functions.
So there is one Python function, which is named len for length,
and you have to open and close parentheses and need to give,
for example, a string of characters like this or a list.
So if I just type "Hello World" like this, here I press enter,
and this, as you can see, this gives us 11, because this Python function,
which is in the core module, in the core Python module,
is going to compute the length of the string here, which is 11.
So we have 11 characters, including the space.
Okay, and don't worry about this.
We are going to come back to that just later.
Here it will just show you what you can do with the Python shell.
So you can write instructions.
You press enter, okay, you can press enter, as you can see here.
I press enter, and whatever is here
will be executed and also evaluated and printed here.