In IDLE, click on File > New File.

This makes the file editor window appear.

Enter the following code: I'll ex[plain what it does afterwards.

# This program says hello

and asks for

my name. Add a blank line, followed by

print('Hello world!')

print('What is your name?')

# ask for their name

myName = input(), print(

'It is good to meet you, ' + myName

print('The length of your name is:')

print(

len(myName))

print('What is your age?')

# ask for their age

myAge = input()

print('You will be ' +

str(int(myAge))

+ 1 +

' in a year.' Save this program as hello.py.

Python programs are just text files that have the .py

file extension. Then click on Run >

Run Module or just press F5 to run the program.

"Hello world! What is your name?" Al.

"It is good to meet you Al. The length of your name is

2. What is your age?" Thirt-

26. Yeeeah.

I am 26. You will be 27 in a year."

Ah, I remember when that was true.

Okay, that's the entire program. One thing to keep in mind

is that Python will start at the first instruction at the top of the program,

and then move downwards executing each instruction entered

Think of it as putting your finger on the top instruction

and as each instruction is executed moving your finger

down to the next instruction. This is just like how you might move your finger

along the lines of a book that you're reading.

Your finger is called the execution. The execution

in Python starts at the top and moves down.

So the first line with the

pound sign is called a "comment". Python ignores comments.

You can use them to write notes to yourself or reminders

about what the code is trying to do or what the entire program does.

Blank lines are completely ignored by Python. You can just use these to space

out your code.

In fact, let's add a couple more blank line right here

just to group together the

code that's relevant to asking for your name, and

the code that ask your age. The

print() function displays the string value inside the parentheses

on the screen. So the line print('Hello world!')

means print out the text in the string 'Hello World!'.

Functions in Python are like mini-programs in your program.

They contain code that you various things and for your convenience Python

comes with a lot of them.

In code, a function is its name,

followed by parentheses and optionally

sometimes there are values passed

to the function inside the parentheses.

In this context these values are called

arguments. But really, values and arguments are the exact same thing.

This is called calling the print() function.

We have code like this here. So the next instruction is also a call

the print() function. This time it's passing the 'What is your name?'

string to the print() function. There's also a comment at the very end of the

line. You can always add comments

to the end of an instruction since everything after that

pound sign will just be ignored by Python. When the input function

is called, Python waits for the user to type some text on a keyboard and

press Enter.

Just like a variable will evaluate to the value it contains,

calls to the input() function evaluate to the string value

of what the user typed. So if I typed in

"Al" when input() was called, this

myName variable assignment statement would just evaluate to 'Al'.

And then the string will get stored inside myName.

Remember, expressions can always evaluate down to a single value.

So if 'Al' is stored in myName

and this is what that call to the print() function looks like

first my name evaluates to the value inside it

and then, this is just a string concatenation,

so the next step looks just like this:

This is the string that gets passed to the print() function call.

This next line introduces a new function called

len(). What len() does is it takes a string

argument and then evaluates

to the integer value of the length of the string,

which is the number characters in a string. Let's just experiment with this

function in the interactive shell for a little bit.

so I can call the len() function and pass it

'Al' and it returns 2.

Or 'Albert' to return 6. Or

length... the blank string and that returns 0.

and then I can just use these function calls to len() anywhere

I could using integer. So I could say, you know,

type out my name ten times, it's length would be 20.

So then we have some more print() and input() calls.

This time we're saving whatever the user types

into the variable myAge. And then we have this line,

which introduces the str()and int() functions.

Now this seems really complicated, so we'll just take this one step at a time

The str() and int() functions return string and integer

values of whatever you pass them. This is really handy if you need to convert

between data types. So in the interactive shell

you can have something like str()

of the value 26, and that returns a string value

with 26 in it. And if you have to go the opposite route,

you can call the int() function and pass it

a string value like '1234' and it will return in integer value.

There's also a float() function that you can use

to convert something to a floating-point value.

So you can pass a string to it, it'll return a float value.

Or if you pass an integer value to it, it will return

a floating-point version value of that

integer. Notice it has the decimal point and .0.

This may seem pointless but remember that the input() function always returns a

string value, even if the string value something like

'26'. We can't do math on a string.

That returns an error. First we have to get in integer value

of it. So that's why we passed it to the

int()function. And just like you can't do addition on strings, you can't do string

concatenation on integers.

So we're going to have to call the str() function

to convert that into a string value. This is What the

entire last line

looks like when it- when Python evaluates it. First

the myAge variable will evaluate to the

value that's inside of it. Then that gets passed to the

int() function, which returns an integer form of it.

We add 1 to that integer. We have to convert that

back to a string value, because we want to concatenate

the other streets next to it. And then after that, it's just the string

concatenation.

And so

all this just reduces down

to this string, which we pass to the print() function call,

which then gets it displayed on the screen. That's how the entire program works.

Just to recap, the file editor is where you type in code for a program.

The execution starts at the top and then proceeds

down, executing each instruction in turn.

Comments begin with a pound sign

and are just notes that are ignored by Python. They're just notes for the

programmer.

Functions are kind of like mini programs that your program can run

to execute some code that does some specialized thing. In this case

the print() function care has code for making strings appear on the screen.

There's a print() function for

making text appear on screen. There's an input() function for getting text from the

keyboard.

And there's also a str(), int(),

and a float() function that returns an integer, string,

or float version the values that we passed them.