Trying to understand Python objects

Fredrik Lundh fredrik at pythonware.com
Wed Nov 22 10:04:31 CET 2006


walterbyrd wrote:

> 1) Can attributes can added just anywhere? I create an object called
> point, then I can add attributes any time, and at any place in the
> program?

in general, yes, but that should be done sparingly.

> 2) Are classes typically created like this:
> 
> class Point:
>   pass
> 
> Then attributes are added at some other time?

no, classes with attributes are typically created like this:

     class Point:
         def __init__(self, x, y):
             self.x = x
             self.y = y

     p = Point(1, 2)

i.e. attributes are created in the initialization function.

> 3) What is with the __underscores__ ??

they're reserved for use by the interpreter, usually for calling special 
methods in you class:

    http://effbot.org/pyref/reserved-identifier-classes
    http://effbot.org/pyref/special-method-names

> 4) Are parameters passed to an class definition?
> 
> class Whatever(params):
>    pass

no, that's the syntax used for inheritance.  arguments passed to the 
class constructor are passed on to the initialization function (see the 
example above).

for more on this, see the tutorial.  Jay Parlar's gentle introduction 
from the community tutorial might be helpful:

     http://effbot.org/pytut/node11-baseline.htm

</F>




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