Non-Programmer's Tutorial for Python 2.6/Hello, World

What you should know
You should know how to edit programs in a text editor or IDLE, save the file and run the file once the files have been saved to your disk.

Printing
Programming tutorials since the beginning of time have started with a little program called "Hello, World!" The syntax changed in Python 3.0. If you are using Python 3.0, you should be reading Non-Programmer's Tutorial for Python 3 instead. So here is the Python 2.6 example:

If you are using the command line to run programs then type it in with a text editor, save it as  and run it with

Otherwise go into IDLE, create a new window, and create the program as in section Creating and Running Programs.

When this program is run here's what it prints:

Hello, World!

Now I'm not going to tell you this every time, but when I show you a program I recommend that you type it in and run it. I learn better when I type it in and you probably do too.

Now here is a more complicated program:

When you run this program it prints out:

Jack and Jill went up a hill to fetch a pail of water; Jack fell down, and broke his crown, and Jill came tumbling after.

When the computer runs this program it first sees the line:

so the computer prints:

Jack and Jill went up a hill

Then the computer goes down to the next line and sees:

So the computer prints to the screen:

to fetch a pail of water;

The computer keeps looking at each line, follows the command and then goes on to the next line. The computer keeps running commands until it reaches the end of the program.

Terminology
Now is probably a good time to give you a bit of an explanation of what is happening - and a little bit of programming terminology.

What we were doing above was using a command called. The  command is followed by one or more arguments. So in this example

there is one argument, which is. Note that this argument is a group of characters enclosed in double quotes ("). This is commonly referred to as a string of characters, or string, for short.  Another example of a string is.

A command and its arguments are collectively referred to as a statement, so

is an example of a statement.

That's probably more than enough terminology for now.

Expressions
Here is another program:

And here is the output when the program is run:

2 + 2 is 4 3 * 4 is 12 100 - 1 is 99 (33 + 2) / 5 + 11.5 is 18.5

As you can see, Python can turn your six hundred dollar computer into a 2 dollar calculator.

In this example, the print command is followed by two arguments, with each of the arguments separated by a comma. So with the first line of the program

The first argument is the string  and the second argument is the mathematical expression , which is commonly referred to as an expression.

What is important to note is that a string is printed as is (the string is what is within the double quotes but doesn't include the double quotes themselves. So the string is printed without the enclosing double quotes.) But an expression is evaluated, (in other words, converted) to its actual value.

Python has six basic operations for numbers:

Notice that division follows the rule, if there are no decimals to start with, there will be no decimals to end with. The following program shows this:

With the output:

14 / 3 = 4 14 % 3 = 2 14.0 / 3.0 = 4.66666666667 14.0 % 3.0 = 2.0 14.0 / 3 = 4.66666666667 14.0 % 3 = 2.0 14 / 3.0 = 4.66666666667 14 % 3.0 = 2.0

Notice how Python gives different answers for some problems depending on whether or not decimal values are used.

The order of operations is the same as in math: So use parentheses to structure your formulas when needed.
 * parentheses
 * exponents
 * multiplication, division  , and remainder
 * addition  and subtraction

Talking to humans (and other intelligent beings)
Often in programming you are doing something complicated and may not in the future remember what you did. When this happens, the program should probably be commented. A comment is a note to you and other programmers explaining what is happening. For example:

Which outputs

3.14285714286

Notice that the comment starts with a hash:. Comments are used to communicate with others who read the program and your future self to make clear what is complicated.

Note that any text can follow a comment, and that when the program is run, the text after the  through to the end of that line is ignored. The  does not have to be at the beginning of a new line:

Examples
Each chapter (eventually) will contain examples of the programming features introduced in the chapter. You should at least look over them and see if you understand them. If you don't, you may want to type them in and see what happens. Mess around with them, change them and see what happens.

Denmark.py

Output:

Something's rotten in the state of Denmark. -- Shakespeare

School.py

Output:

First Grade 1 + 1 = 2 2 + 4 = 6 5 - 2 = 3 Third Grade 243 - 23 = 220 12 * 4 = 48 12 / 3 = 4 13 / 3 = 4 R 1 Junior High 123.56 - 62.12 = 61.44 (4 + 3) * 2 = 14 4 + 3 * 2 = 10 3 ** 2 = 9

Exercises

 * 1) Write a program that prints your full name and your birthday as separate strings.
 * 2) Write a program that shows the use of all 6 math functions.