Decorator to pass instance and class to method

Question

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.
 """
 @wraps(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)
 ...
 @with_class
 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
 else:
 annotation_selector = cls.annotation == self.annotation
 try:
 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.

• bipll: So, you saved typing a single line at the expense of typing a single line? :-\
• Richard Neumann: @bipll Good point.

Answer 1

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__).

Take:

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)