Comments can be added to computer programs. A comment is human readable text that is not executed by Python.

## Single line comments

Single line comments can be added using the numbersign:

```# Show the world a message print('Hello World')```

If you want to add stories or a few sentences, Python offers two ways:

```# Calculate the sum of x+y # Used in calculator app z = x + y```

Another accepted method is:

```''' We can type multiple lines of commment if we use the indicator. '''```

## Math operations

Python has support for both mathematical operations and functions.

Mathematical operations
An overview of operations:

Operation Result
x + y sum of x and y.
x * y multiplication of x and y.
x – y difference of x and y.
x / y division of x by y.
x % y remainder of x/y
x ** y x to the power of y
abs(x) absolute value of x
sqrt(x) square root of x

Mathematical functions
Python supports a wide variety of mathematical functions.

Function Returns Example
abs(x) Returns the absolute value of x.
```x = -35 x = abs(x) print(x)```
cmp(x,y) Returns -1 if x < y
Returns 0 if x equals to y
Returns 1 if x > y.
```x = 6 y = 4 print( cmp(x,y) )```
exp(x) Returns the exponential of x
```import math x = 6 print( math.exp(x) )```
log(x) The natural logarithm of x
```import math x = 6 print( math.log(x) )```
log10(x) The base-10 logarithm of x
```import math x = 6 print( math.log10(x) )```
pow(x,y) The result of x**y
```import math x = 6 print( math.pow(x,2) )```
sqrt(x) The square root of x
```import math x = 6 print( math.sqrt(x) )```
Tip
You can use the Python interpreter as calculator. To do so you simply start Python without an IDE and filename. Example:

```  Python 2.7.6 (default, Jun 22 2015, 17:58:13)
[GCC 4.8.2] on linux2
>>> 18*17
306
>>> 2**4
16
>>>
```

## Install a Python IDE

An Integrated Desktop Environment (IDE) is a software application for programming. In addition to simple text editing they have all kind of features such as syntax highlighting, code completion, tabs, a class browser and many more.

#### Online Python Interpreters

The online interpreters may not work for everything but will work for most of the beginner tutorials. I recommend using a desktop IDE or the official Python interpreter.

Overview of IDEs (You only need one)