"Wojciech Gryc" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
| Hi,
|
| I recently started using Python and am extremely happy with how
| productive it's made me, even as a new user. I'm hoping to continue
| using the language for my research, and have come across a bit of a
| stumbling block.
|
| I'm a seasoned Java programmer and quite a big fan of interfaces...
| i.e. The idea that if I make a number of distinct classes that
| implement interface X, I can pass them all as parameters to functions
| or whatnot that require an X object.
|
| Is there something similar in Python?
As others have noted, without typechecks, Python code is generic. For
example, 'a+b' means "Try a.__add__(b). If that does not work, try
b.__radd__(a). If that does not, raise an error."
| What I'd like to do is create a feature detection system for my work
| -- specifically, a general class / interface called "Feature" and then
| subclasses that implement functions like isFeaturePresent() in all of
| their different and unique ways. I'd love to hear how I can do this in
| Python.
If you have several methods (with multiple implementations), an abstract
base class can be helpful:
class Feature(object):
def isFeaturePresent(self):
raise NotImplementedError
def otherMethod(self):
raise NotImplementedError
# etc
Inherit from Feature (and possibly other classes -- Python has multiple
inheritance) to make your subclasses. Then put 'if not isinstance(arg,
Feature): raise TypeError(func requires Features)' at the top of functions
that work on Features. If you call Feature methods more than once in a
function, this save multiple checks or try-except blocks.
The cost, of course, is the inheritance requirement.
Terry Jan Reedy
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