Python classes: Simplify?

Jean-Michel Pichavant jeanmichel at sequans.com
Fri Mar 23 15:19:55 CET 2012


Steven Lehar wrote:
> It seems to me that the Python class system is needlessly confusing. 
> Am I missing something?
>
> For example in the class Complex given in the documentation
>
> *class Complex:*
> *    def __init__(self, realpart, imagpart):*
> *        self.r = realpart*
> *        self.i = imagpart*
> *
> *
> *x = Complex(3.0, -4.5)*
>
> I initially found it profoundly confusing that __init__( ) calls for 3 
> arguments, but you call Complex( ) with 2. Furthermore, why not call 
> the initialization function after the class name as is done in other 
> languages? Isn't that the simplest conceptually? Demonstrating with 
> the above example:
>

In python, writting obj.method() will be translated into method(obj) so 
any instance method has a #arg + 1 arguments, something you'll get 
familiar with.
Furthermore, Complex(3.0, -4.5) invokes 2 functions : __new__ and 
__init__. __new__ is the "constructor", this is the function that 
returns an instance. __init__ is an initializer, at the time it's called 
the instance already exists and is viable.


> *class Complex:*
> *    def Complex(realpart, imagpart):*
> *        Complex.r = realpart*
> *        Complex.i = imagpart*
> *
> *
> *x = Complex(3.0, -4.5)*
> *
> *
> Is there a good reason why classes cannot be defined that way? 
> (Besides the problem of backward-compatibility)
>


Python uses a different data model, it is a very good idea to mark 
theses differences using an explicit distinct syntax so that people 
won't jump into false conclusions like "it's like C or Java". It is not.

JM

JM



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