CODEWITHSUNDEEP
pythonclassinheritance
ellie ff1493
ellie ff1493

Reputation: 125

return new instance of current class

i'd like to return a new instance of the current class, when an inherited class return it will return the base class instead of the current class

class class1:
    def __init__(self):
        self.foo = 1
        self.bar = 2
    def new(self):
        return class1()

class class2(class1):
    def __init__(self):
        super().__init__()

c1 = class1()
c2 = class2()
print(c1.new())
print(c2.new())

this returns

<main.class1 object at 0x0000027B681E57F0>
<main.class1 object at 0x0000027B681E57F0>

desired result

<main.class1 object at 0x0000027B681E57F0>
<main.class2 object at 0x0000027B681E57F0>

Upvotes: 1

Views: 4953

Answers (3)

theodox
theodox

Reputation: 12208

you can get the current class like this:

class class1:
    def __init__(self):
        self.foo = 1
        self.bar = 2
    def new(self):
        return self.__class__()

Inheritors will return their own classes. You will have to handle the logic for any different __init__ signatures yourself, however. A classmethod would be a better design choice unless you needed information from the current instance to create the new one.

Upvotes: 1

NPE
NPE

Reputation: 500317

You could use __class__ for that:

class class1(object):
    def new(self):
        return self.__class__()

class class2(class1):
    pass

c1 = class1()
c2 = class2()
print(c1.new())
print(c2.new())

Upvotes: 4

chepner
chepner

Reputation: 531075

Define a class method instead:

class Class1:
    def __init__(self):
        self.foo = 1
        self.foo = 2

    @classmethod
    def new(cls):
        return cls()

class Class2(Class1):
    pass

Now when you call c2.new(), the runtime will see that Class2 has no method named new, but Class1 does. Further, Class2 will be passed as the implicit argument to new, not Class1.

The class method is more appropriate than an instance method because you don't have any other interest in the object invoking the method beyond what class it is.

Upvotes: 3

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