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Re: Difference method vs attribut = function

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  Re: Difference method vs attribut = function "Peter J. Holzer" <hjp-python@hjp.at> - 2024-06-29 21:53 +0200

#196347 — Re: Difference method vs attribut = function

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On 2024-06-28 18:08:54 +0200, Ulrich Goebel via Python-list wrote:
> a class can have methods, and it can have attributes, which can hold a
> function. Both is well known, of course.
> 
> My question: Is there any difference?
> 
> The code snipped shows that both do what they should do. But __dict__
> includes just the method,

The other way around: It includes only the attributes, not the methods.

> while dir detects the method and the
> attribute holding a function. My be that is the only difference?
> 
> 
> class MyClass:
>     def __init__(self):
>         functionAttribute = None
>         
>     def method(self):
>         print("I'm a method")
> 
> def function():
>     print("I'm a function passed to an attribute")

Here is the other main difference: The object is not passed implicitely
to the function. You have no way to access mc here.

You can create a method on the fly with types.MethodType:

import types
mc.functionAttribute = types.MethodType(function, mc)


> By the way: in my usecase I want to pass different functions to
> different instances of MyClass. It is in the context of a database app
> where I build Getters for database data and pass one Getter per
> instance.

Or in this case, since each function is specific to one instance, you
could just use a closure to capture the object. But that might be
confusing to any future maintainers (e.g. yourself in 6 months), if the
method doesn't actually behave like a method.

        hp

-- 
   _  | Peter J. Holzer    | Story must make more sense than reality.
|_|_) |                    |
| |   | hjp@hjp.at         |    -- Charles Stross, "Creative writing
__/   | http://www.hjp.at/ |       challenge!"

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