[Tutor] Creating instance of child classes dynamically

[Alan Gauld]

On 07/02/2021 15:18, Sachit Murarka wrote:
> I meant base class in a different python file. It was a typo.
> 
> Example :
> 
> parent.py
> class Parent():
>     @abstractmethod
>     def process(self):
> 
> child1.py
> class Child1():
>       def process(self):
>           #Doing something
> 
> child2.py
> class Child2():
>       def process(self):
>           #Doing something else
> 
> 
> My use case is , Parent will define the template. On the run type user will
> pass a string , eg String will be child1 or child2 etc. Accordingly we want
> to call process function of that class.

OK, that's all pretty standard although a dictionary of functions
keyed by string is probably a more effective way to do it.

> Please note each child class is in a different file . In actual solution
> there will be many children and we can not put all children in a single py
> file.

Best practice in Python is to keep related classes in a single
module to minimize dependencies. But you don;t want a huge number of
classes in a single module, I agree.

> As using reflections we can create objects at run time by giving fully
> qualified class names(Atleast in java). I have worked in Java not in Python
> much, so trying to achieve something similar.  In java we used to do this:
> 
> String input="Child1";
> Parent p = Class.forName(input);
> p.process() // this will call the method of base class which was stored in

In Pyton classes are objects so you can just assign the class to a
variable or put it in a dictionary so:

import child1, child2
# Store classes
classes = { "Child1": child1.Child1(), "Child2": child2.Child2,...}

classname = "Child1"
classes["Child1"]().process()  # calls process on an instance of Child1

But as I said functions might be more effective here:

def func1():...
def fuc2():...
etc...

funcs = {"Child1":func1,"Child2":func2

funcs[input]()

There's no point in creating classes just for the sake of it.
OTOH if your classes have several other methods than just
process() and they share the common data of the instance
then they might make sense.

-- 
Alan G
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