[Tutor] design advice for function

[Alan Gauld]

> def adder(**args):
>    argsList = args.values()
>    sum = argsList[0]
>    for x in argsList[1:]:
>        sum = sum + x
>    return sum

> line 3, in adder
>    sum = argsList[0]
> IndexError: list index out of range
> 
> This is caused by the line: print adder().  Obviously
> if adder() doesn't receive any arguments, it can't
> build the lists resulting in an IndexError.  What is
> the best way to solve this?  Should I write some
> syntax into the function to check for arguments? 

The Pythonic way is to use exceptions.

You can either handle the exception inside the function 
or outside:

def adder(**args):
  try:
      # your code hee
  except IndexError: 
     return 0  # or some other default, perhaps even None?!

OR

def adder(**args):

  try:
      # your code hee
  except IndexError: 
     raise

try:
   print adder()
   print addre(a=1)
   # etc...
except IndexError:
   print 'oops, no arguments to adder'

In this case I'd probably use the first approach (with None as default), 
but its up to you...

Alan G