Checking for required arguments when instantiating class.

[Lie Ryan]

Lacrima wrote:
>>>>> class First:
>>         def __init__(self, *args, **kwargs):
>>                 pass
>>
>>>>> class Second:
>>         def __init__(self, somearg, *args, **kwargs):
>>                 self.somearg = somearg
>>
>> How can I test that First class takes 1 required argument and Second
>> class takes no required arguments?
> 
> 
> Sorry, I have made a mistake. Of course, Second class takes 1 required
> argument, not First.

Of course, it is possible to just try it one-by-one with a try block and 
a while loop (as long as your class/function doesn't rely/change on some 
global state (e.g. files, global variable, GUI, etc) while 
initializing/called), but if you really need that, there is something 
seriously wrong with the class/function design. You should check the 
help and determine how many and what are all the arguments meant.

In case you're wondering, this is how it would look like:

 >>> def f0():
...     print
...
 >>> def f1(a):
...     print a
...
 >>> def f2(a, b):
...     print a, b
...
 >>> def f2a(a, b, *args, **kargs):
...     print a, b, args, kargs
...
 >>> import itertools
 >>> funclist = [f0, f1, f2, f2a]
 >>> for f in funclist:
...     for i in itertools.count():
...         try:
...             f(*range(i))
...         except TypeError:
...             pass
...         else:
...             print 'Function %s takes %s required arguments' % 
(f.__name__, i)
...             break
...

Function f0 takes 0 required arguments
0
Function f1 takes 1 required arguments
0 1
Function f2 takes 2 required arguments
0 1 () {}
Function f2a takes 2 required arguments
 >>>