The def statement creates a function object and assigns it to a name.
Its general format is as follows:
def name(arg1, arg2,... argN): statements
Function bodies often contain a return statement:
def name(arg1, arg2,... argN): ... return value
Python return statement can show up anywhere in a function body.
When return statement is reached, it ends the function call and sends a result back to the caller.
The return statement consists of an optional object value expression that gives the function's result.
If the value is omitted, return sends back a None.
The return statement itself is optional too.
If it's not present, the function exits when the control flow falls off the end of the function body.
Technically, a function without a return statement also returns the None object automatically.