CODEWITHSUNDEEP
python
Nadia
Nadia

Reputation: 81

How do I pass a whole class as a parameter to another class`s method

Is it possible to pass a whole class (not an instance) as a parameter to another class method in Python? If I have several instances of the class first and need to pass any of them not specifying which one to method of class Second, can I do something like this:

class First():
    def __init__(self, a, b):
        pass

class Second():
    def __init__(self, c, d):
        pass
    def method(self, First):
        #and how do I call here the whole class First
        #without calling a particular instance here?

Upvotes: 2

Views: 8608

Answers (3)

Angelo Mendes
Angelo Mendes

Reputation: 978

You can do:

class Model1:

    def get():
        return '1'

class Model2:
    def get(Model1):
        print('test: '+ str(Model1.get()))

if __name__ == '__main__':
    Model2.get(Model1)

the output is;: test: 1

Upvotes: 0

abarnert
abarnert

Reputation: 365737

First, you don't need to specify types in Python. So, if you want method to take a First instance, just do this:

class Second():
    def __init__(self, c, d):
        pass
    def method(self, first):
        pass

my_first = First(0, 1)
my_second = Second(2, 3)
my_second.method(my_first)

I believe that answers your real question, which is:

If I have several instances of the class first and need to pass any of them not specifying which one to method of class Second…

If you want to ensure that the parameter actually is a First, you can always add an assert isinstance(first, First) or if not isinstance(first, First): raise TypeError or whatever, but usually you don't want to do that in Python. The whole point of "duck typing" is that you write a function that takes "anything that acts like a First instance" rather than a function that takes "a First instance".

You then say:

Now I need to mutate variables from the First class inside the method of a second class:

So… just do it. Your example doesn't have any attributes in the First class, so let's add some:

class First():
    def __init__(self, a, b):
        self.total = a + b

And now, let's use them in Second.method:

class Second():
    def __init__(self, c, d):
        self.total = c + d
    def method(self, first):
        first.total += self.total

So:

>>> my_first = First(0, 1)
>>> my_first.total
1
>>> my_second = Second(2, 3)
>>> my_second.total
5
>>> my_first.total += 2
>>> my_first.total
3
>>> my_second.method(my_first)
>>> my_first.total
8

Or, if you meant that you wanted to mutate the class attributes in class First… you don't even need a First instance for that:

First.my_class_attribute = 1

If you really do need to pass a class itself… well, a class is a regular value like anything else:

class Second():
    def __init__(self, c, d):
        pass
    def method(self, cls):
        pass

my_second = Second(1, 2)
my_second.method(First)

And you can access the class attributes of cls from within method, just as easily as you can access instance attributes when an instance is passed.

Upvotes: 3

J0HN
J0HN

Reputation: 26941

Straightforward.

def method(self, First):
    First() #instantiation
    First.classmethod()
    First.staticmethod()

In python classes are objects itself, so you are able to call your method like this

second_instance.method(Any_Class_You_Want)

Upvotes: 3

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