Function Defaults - avoiding unneccerary combinations of arguments at input

[Terry Reedy]

On 3/25/2015 1:43 PM, Ivan Evstegneev wrote:
> Hello all ,
>
>
> Just a little question about function's default arguments.
>
> Let's say I have this function:
>
> def  my_fun(history=False, built=False, current=False, topo=None,
> full=False, file=None):
> 	if currnet and full:
> 		do something_1
> 	elif current and file:
> 		do something_2
> 	elif history and full and file:
> 		do something_3
> 	
>
> 	...... some code here..............
>
> and so on...
>
> I won't cover all the possibilities here (actually I don't use all of them
> ^_^).
>
> The question is about avoiding the response for unnecessary combinations?
>
> For instance, if user will call function this way:
>
>
>>>> my_fun(current=True, full=True, topo='some str', file="some_file")
>
> That will lead to function's misbehavior. As a particular case it will
> choose "current and full" condition.
>
>
> What is the common accepted way to deal with such unwanted situations?

Raise a value error for illegal combinations.  There are a few instances 
in the stdlib where 2 of several options are mutually incompatible.


-- 
Terry Jan Reedy