In mathematics, a function is written as a map that uniquely assigns to every element 
from the domain 
a corresponding element 
from the range 
.
This is expressed by 
.
Alternatively, when considering particular elements 
and 
, you write 
.
Here, 
is called the name of the function and 
is its value when applied to 
. Here, 
is sometimes called the argument of 
. Let's first look at an example before considering functions in Python.
For example, 
and 
. This function maps two real numbers to their difference.
In mathematics, functions can have numbers, vectors, matrices, and even other functions as arguments. Here is an example of a function with mixed arguments:
In this case, a real number is returned. When working with functions, we have to distinguish between two different steps:
- The definition of the function
- The evaluation of the function, that is, the computation of
for a given value of 
The first step is done once, while...