Question

I want to implement my own copy method for a class A which looks like this:

class A(object):
    def __init__(self):
        self.field1 = generate_a_list_of_ints()
    def __copy__(self):
        result = A()
        result.fiel1[:] = self.field1[:]
        return result

The problem with the code above is that when copying an A object, the initialization code will be invoked even though there is no need to get the initial values.

How can I copy the field1 without running initialization code? I looked for information about __new__ but most of it was referring to factories and stuff that seemed unrelated, so it’s still unclear to me how to skip the initialization.

Answer 1

I suggest an optional argument in your __init__() method, like so:

class A(object):
    def __init__(self, init=True):
        if init:
            self.field1 = generate_a_list_of_ints()
    def __copy__(self):
        result = A(init=False)
        result.fiel1[:] = self.field1[:]
        return result