Object not iterable in python when created made class iterable for objects

Question

I am making a program where I need to iterate through every option in a class to perform actions to each object, to do that I made an 'IterRegistry' Class to turn the metaclass of my objects to iterable but for some reason, it still isn't working.

class IterRegistry(type):
    def __iter__(cls):
        return iter(cls._registry)


class TreeLine(object):
    __metaclass__ = IterRegistry
    _registry = []

    def __init__(self, earnings, buy_price):
        self._registry.append(self)
        self.earnings = earnings
        self.buy_prince = buy_price


TreeLine(0, 0)
TreeLine(0, 7)

for i in TreeLine:
    print(i)

I just get the error message: File "/Users/PycharmProjects/AISTUFF/venv/[email protected]", line 23, in for i in TreeLine: TypeError: 'type' object is not iterable

You need to make your class iterable, see stackoverflow.com/questions/21665485/… — luis.parravicini
– luis.parravicini, Commented Oct 15, 2019 at 10:54

snakecharmerb · Accepted Answer · 2019-10-15 11:25:16Z

1

Declaring a class metaclass like this:

class TreeLine(object):
    __metaclass__ = IterRegistry

does not work in Python 3. Instead, the metaclass is declared like this:

class TreeLine(metaclass=IterRegistry):
    ...

The syntax is documented here. The change was proposed in PEP3115.

Note that the __metaclass__ form is not invalid syntax, it just doesn't behave as in Python 2.

>>> class M(type):pass
... 
>>> class C:
...     __metaclass__ = M
... 
>>> type(C)
<class 'type'>
>>> class D(metaclass=M):pass
... 
>>> type(D)
<class '__main__.M'>
>>>

answered Oct 15, 2019 at 11:25

snakecharmerb

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