# How to: A simple Python Function example

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Functions in Python can be simple or extraordinarily complex. This will teach you how to write a simple Python Function example. From there you can go on to build much more complex functions.

Here is an example of a Python function that multiplies an number by itself.
``` def double(number): dbl_num = number * number return dbl_num ```

def is define. So we are defining our number in Python for this function. The first line stores the number and in the second line we store the number as a new variable called dbl_num. The above function in Python will not do anything by itself. You need an input either defined in your function or asked as an input by the user.

Here is a function you can run and test:
``` def double(number): dbl_num = number * number return dbl_num```

``` ```

```number_in = 10 number_out = double(number_in) print(number_out) ```

Here is what we just did. This example of a Python function is the same as above what changed is we now have a number to multiple. The number_in is 10. We needed to take that number and put it into our function, thus, double(number_in). We made that equal to a new variable of number_out. Then we printed the number_out which results in 100.