Math in Python

Code Example 1 

Hello, world!

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

What happened? You just created a program, that prints the words 'Hello, world'. The IDLE environment that you are in immediately compiles whatever you have typed in. 

Code Example 2 – Maths

>>> 1 + 1
2

>>> 20 + 80
100

>>> 18294 + 449566
467860
(These are additions.)

>>> 6 - 5
1
(Subtraction)

>>> 2 * 5
10
(Multiply, rabbits!)

>>> 5 ** 2
25
(Exponentials; e.g., this one is 5 squared)

>>> print "1 + 2 is an addition"
1 + 2 is an addition
(The print statement, which writes something onscreen. Notice that 1 + 2 is left unevaluated.)

>>> print "One kilobyte is 2^10 bytes, or", 2 ** 10, "bytes."
One kilobyte is 2^10 bytes, or 1024 bytes.
(You can print sums and variables in a sentence.
        The commas separating each section are a way of
        separating clearly different things that you are printing.)

>>> 21 / 3
7

>>> 23 / 3
7
(Division; note that Python ignores remainders/decimals.)

>>> 23.0 / 3.0
7.666666666666667
(This time, since the numbers are decimals themselves, the answer
        will be a decimal.

>>> 23 % 3
2

>>> 49 % 10
9
(The remainder from a division)

As you see, there is the code, then the result of that code. I then explain them in brackets. These are the basic commands of Python, and what they do. Here is a table to clarify them (because tables look cool, and make you feel smarter ;) ):

Table 1 – Python operators

Command	Name	Example	Output
+	Addition	4 + 5	9
-	Subtraction	8 - 5	3
*	Multiplication	4 * 5	20
/	Division	19 / 3	6
%	Remainder (modulo)	19 % 3	1
**	Exponent	2 ** 4	16

Remember that thing called order of operations that they taught in maths? Well, it applies in Python, too. Here it is, if you need reminding:

1. parentheses ()
2. exponents **
3. multiplication *, division \, and remainder %
4. addition + and subtraction -

Order of Operations [edit]

Here are some examples that you might want to try, if you're rusty on this:

Code Example 3 – Order of operations

>>> 1 + 2 * 3
7
>>> (1 + 2) * 3
9

In the first example, the computer calculates 2 * 3 first, then adds 1 to it. This is because multiplication has the higher priority (at 3) and addition is below that (at a lowly 4).

In the second example, the computer calculates 1 + 2 first, then multiplies it by 3. This is because parentheses (brackets, like the ones that are surrounding this interluding text ;) ) have the higher priority (at 1), and addition comes in later than that.

Code Example 4 – Parentheses

>>> 4 - 40 - 3
-39
>>> 4 - (40 - 3)
-33

Code Example 5 – Comments

>>> #I am a comment. Fear my wrath!

>>>

A comment is a piece of code that is not run. In Python, you make something a comment by putting a hash (#) in front of it. A hash comments everything after it in the line, and nothing before it. So you could type this:

Code Example 6 – Comment examples

>>> print "food is very nice" #eat me
food is very nice
(A normal output, without the smutty comment,
thank you very much)

>>># print "food is very nice"

(Nothing happens, because the code was after a comment)

>>> print "food is very nice" eat me

(You'll get a fairly harmless error message,
because you didn't put your comment after a hash)

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