Baby Steps to Metaclasses in Python3

I will start this lesson by talking about some basics of the python type system and the introduce the concept of META-CLASSES afterwards.

To start out lets look at these basic examples:

So every single thing you create in python has a type associated with it. from the example above the variable name is of type

str 

(

string

) and age is of type

int 

(

integer

) and however each of these variables has a property or attribute of

__class__ 

which in most cases we call a magic method in python, this attribute is the class which is instantiated in the creation of variables and in other word it is the type of the variable. so therefore

type(name) 

and

name.__class__

will return the same data which is

str 

(

string

) for the variable

name 

in this case.

see:

However this idea also extends to the classes you create yourself.

see:

Based on the example we see that the variable

me 

is of type

User 

and the type is essentially the class we instantiated initially, so to create a new instance we use the class name and the expected parameters or arguments which will later be the associated type. However classes also have types associated with them.

see:

Therefore the class

User 

is of type

type 

which means the type class was instantiated with it's expected parameter which python takes care of to create the class

User

. Moreover the parameters which the

type 

class takes are

(clsname,bases,methods)

, so lets see how it all works behind the scenes.

see:

So essentially what python does is that when you create a class it take the

clsname, bases and the functions or methods

and feeds it to the class

type

.

So why meta-classes, it turns out that the class

type 

is actually something that you can customize and modify. Well the question is how do we do that. The way we can modify classes is through inheritance. i.e

see:

with that done i think we are all set!!!!!. so lets go for a test drive

see:

As we can see this works almost as exact as the class type. if you notice when creating the a new class with the

custom_type_class 

we created it had to print out a little info before making the class, which means the class was created through the

custom_type_class 

we created earlier, so therefore the class above is an example of what is called a META-CLASS.

So a simple definition of a meta-class will be:

An alternate way to monitor or supervise what happens in class definition

So what python provides is a way to use the above in class definition i.e

Basically when creating a class the default parameter for the

metaclass 

argument is the class

type

and we don't want that so we modify that by using the

custom_class_type 

we created earlier as the argument for

metaclass 

so therefore the class

User 

will be create with the

custom_class_type

.

Conclusion

And that’s all! You just learned the basics of meta-classes using python.Thanks for following along! If you liked this, give this story a couple of reactions so more people can see it!

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