[Tutor] Function not returning 05 as string

[Steven D'Aprano]

On Mon, Apr 13, 2015 at 08:11:46AM -0400, Ken G. wrote:
> I am sure there is an simple explanation but when I input
> 5 (as integer), resulting in 05 (as string), I get zero as the end
> result. When running the code:

> number01 = 0

Here you set the variable "number01" to the int 0.

> numberentry()

Here you call the function. It returns "05", but you don't do anything 
with it, so it just gets dropped on the floor and thrown away.

> print
> print number01

Here you print the variable number01, which is still the int 0, 
unchanged.

I think where you are mislead is that you are not aware, or have 
forgotten, that global variables and local variables are different. So a 
variable "x" outside of a function and a variable "x" inside a function 
are different variables. Think of functions being like Los Vegas: "what 
happens in Vegas, stays in Vegas" -- function local variables don't leak 
out and have effects outside of the function except via the "return" 
statement, and even then only if the caller assigns the result to 
another variable:

function()  # return result is thrown away
x = function()  # return result is assigned to x


The other way to have an effect outside of the function is to use global 
variables, and the global keyword. This is occasionally necessary, but I 
strongly recommend against it: it is poor programming practice and a bad 
habit to get into.


-- 
Steve