using attributes as defaults

Jean-Michel Pichavant jeanmichel at sequans.com
Tue Feb 8 11:19:16 CET 2011


Westley Martínez wrote:
> On Fri, 2011-02-04 at 13:08 -0800, Wanderer wrote:
>> I want to give the option of changing attributes in a method or using
>> the current values of the attributes as the default.
>>
>> class MyClass():
>>      """  my Class
>>      """
>>      def __init__(self):
>>           """ initialize
>>           """
>>           self.a = 3
>>           self.b = 4
>>
>>      def MyMethod(self, a = self.a, b = self.b)
>>           """ My Method
>>           """
>>           self.a = a
>>           self.b = b
>>           DoSomething(a, b)
>>
>> The above doesn't work. Is there a way to make it work?
>>
>> Thanks
>>
>>     
> This doesn't work because you can't reference keyword arguments in the 
> keyword argument array. This will work:
> class MyClass:
>
>     def __init__(self):
>         """ initialize
>
>         Really? These are the worst docstrings ever.
>
>         """
>         self.a = 3
>         self.b = 4
>
>     def MyMethod(self, a=None, b=None)
>         if a is not None:
>             self.a = a
>         if b is not None:
>             self.b = b
>         DoSomething(a, b) 
There is an alternative to this None thing:

Don't use optional arguments. Optional arguments are fine ,but I found 
myself avoiding using them is often a better choice.
Quoting the zen of  python: "Explicit is better than implicit."
If the reason for using optional arguments is that it'll take you 2 sec 
less to write the method call, then it sounds kind of wrong. Any other 
reason would be valid I guess.

I personnaly use optional arguments only to keep backward compatibility 
when changing a method signature.

JM




More information about the Python-list mailing list