guides/training_with_built_in_methods.py/CategoricalTruePositives/__init__
class CategoricalTruePositives:    def __init__(self, name="categorical_true_positives", **kwargs):
        super().__init__(name=name, **kwargs)
        self.true_positives = self.add_variable(
            shape=(), name="ctp", initializer="zeros"
        )