python: are property fields being cached automatically?

Question

My question is are the following two pieces of code run the same by the interpreter:

class A(object):
  def __init__(self):
     self.__x = None

  @property         


        

Answer 1

The decorator from Denis Otkidach mentioned in @unutbu's answer was published in O'Reilly's Python Cookbook. Unfortunately O'Reilly doesn't specify any license for code examples – just as informal permission to reuse the code.

If you need a cached property decorator with a liberal license, you can use Ken Seehof's @cached_property from ActiveState code recipes. It's explicitly published under the MIT license.

def cached_property(f):
    """returns a cached property that is calculated by function f"""
    def get(self):
        try:
            return self._property_cache[f]
        except AttributeError:
            self._property_cache = {}
            x = self._property_cache[f] = f(self)
            return x
        except KeyError:
            x = self._property_cache[f] = f(self)
            return x

    return property(get)

Answer 2

No, the getter will be called every time you access the property.