In some of my peewee-based ORM models, I need to access the instance as well as the respective class. Since I caught myself always repeating the line cls = self.__class__ at the top of each such methods, I wrote a decorator for that:

def with_class(function):
    """Adds the instance's class as second
    parameter to the wrapped function.

    def wrapper(self, *args, **kwargs):
        """Wraps the given function."""
        return function(self, self.__class__, *args, **kwargs)

    return wrapper

Example use case:

class Location(_TerminalModel):
    """Location of a terminal."""

    address = CascadingFKField(Address, column_name='address')
    annotation = CharField(255, null=True)


    def save_unique(self, cls, *args, **kwargs):
        """Saves the location if it is new or
        returns the appropriate existing record.
        if self.annotation is None:
            annotation_selector = cls.annotation >> None
            annotation_selector = cls.annotation == self.annotation

            return cls.get((cls.address == self.address) & annotation_selector)
        except cls.DoesNotExist:
            self.save(*args, **kwargs)
            return self

I'd like to have critique on this solution and am open to alternatives.

  • 3
    \$\begingroup\$ So, you saved typing a single line at the expense of typing a single line? :-\ \$\endgroup\$ – bipll Jul 23 '18 at 13:19
  • \$\begingroup\$ @bipll Good point. \$\endgroup\$ – Richard Neumann Jul 23 '18 at 13:26

I'd recommend not using value.__class__. This is as it's not guaranteed to return the type.

type(x) is typically the same as x.__class__ (although this is not guaranteed – a new-style class instance is permitted to override the value returned for x.__class__).


class A:
    __class__ = 'something'

print(A.__class__)   # <class 'type'>
print(A().__class__) # 'something'
print(type(A()))     # <class '__main__.A'>

I also think just using type would be cleaner, and easier to understand.

def save_unique(self, *args, **kwargs):
    cls = type(self)

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