[Tutor] Function behavior

[Ken Green]

Thanks Alan.  With suggestion and help from several other people on the 
list, I was able to solve the problem.  I learned from an example 
previously given.  I am using several different tutorials and I have 
yours bookmarked.

Ken

On 09/16/2010 05:26 PM, Alan Gauld wrote:
>
> "Ken Green" <beachkidken at gmail.com> wrote
>
>> I am unclear on the behavior of using a function.
>
> You certainly are!
> Which tutorial are you working from?
> You have several fundamental errors here, its hard to know
> where to start.
>
>> def change(amount):
>>     if match == 1:
>>         amount = 0
>>     if match == 2:
>>         amount = 0
>>     if match == 3:
>>         amount = 3
>
> This function is called change and it has an input parameter called 
> amount.
> The parameter is like a local variable only visible inside the function.
> Because there are no return statements in it it will always return the
> default value of None - probably not what you want.
>
> Inside the function you compare a variable called match - which is not
> defined in the function so presumably will be found outside in the module
> or global scope - to a number.
> You then set the parameter amount to another number, one greater
> than the test value. But since amount is the parameter and invisible
> outside the function that will have no affect on anything outside the
> function.
>
>> match = raw_input("How many matches?: ")
>
> Now we define the global variable match but set it to a string.
> The change() function is expecting match to be a number.
> Maybe we should convert it using int()?
>
>> change(match)
>
>
> This does nothing and since we don't assign the functions value
> to anything the None that it returns is lost.
>
>> print amount
>
> amount is not defined anywhere at the global scope and
> the amount parameter in the function is not visible outside
> the function.
>
>> How many matches?: 2
>> Traceback (most recent call last):
>>   File "/home/ken/Python262/TEST Function.py", line 13, in <module>
>>     print amount
>> NameError: name 'amount' is not defined
>
>> Should it be def change(match) instead of def change(amount)?
>> Perhaps, change(amount) instead of change(match)?
>
> You need to go back to basics on how parameters and arguments
> work (This is, I admit, a subtle concept when you first come across it)
>
>> Perhaps, I need to add return somewhere?
>
> Yes you probably do. You can do what you want without it but
> its considered bad practice. Functions should reurn their results.
>
> Try reading the functions and modules topic in my tutorial
> to see if that helps.
>