Empty class object in Python

Question

I'm teaching a Python class on object-oriented programming and as I'm brushing up on how to explain classes, I saw an empty class definition:

class Employee:     pass 

The example then goes on to define a name and other attributes for an object of this class:

john = Employee() john.full_name = "john doe" 

Interesting!

I'm wondering if there's a way to dynamically define a function for an instance of a class like this? something like:

john.greet() = print 'Hello, World!' 

This doesn't work in my Python interpreter, but is there another way of doing it?

Answer 1

A class is more or less a fancy wrapper for a dict of attributes to objects. When you instantiate a class you can assign to its attributes, and those will be stored in foo.__dict__; likewise, you can look in foo.__dict__ for any attributes you have already written.

This means you can do some neat dynamic things like:

class Employee: pass def foo(self): pass Employee.foo = foo 

as well as assigning to a particular instance. (EDIT: added self parameter)

Answer 2

Try with lambda:

john.greet = lambda : print( 'hello world!' ) 

The you'll be able to do:

john.greet() 

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EDIT: Thanks Thomas K for the note - this works on Python 3.2 and not for Python2, where print appeared to be statement. But this will work for lambdas, without statements (right? Sorry, I know only python3.2 (: )