[Python-Dev] class name spaces inside an outer function (original) (raw)

Ethan Furman ethan at stoneleaf.us
Sun Apr 28 08:10:42 CEST 2013

On 04/27/2013 09:20 PM, Guido van Rossum wrote:

On Saturday, April 27, 2013, Greg Ewing wrote:

This whole business can be avoided by doing things differently in the first place. Instead of initialising the enum items by calling the class, just assign a tuple of args to the name and have the metaclass make the constructor call. class Planet(Enum): MERCURY = (3.303e+23, 2.4397e6) VENUS = (4.869e+24, 6.0518e6) EARTH = (5.976e+24, 6.37814e6) MARS = (6.421e+23, 3.3972e6) JUPITER = (1.9e+27, 7.1492e7) SATURN = (5.688e+26, 6.0268e7) URANUS = (8.686e+25, 2.5559e7) NEPTUNE = (1.024e+26, 2.4746e7) def init(self, mass, radius): self.mass = mass self.radius = radius I think that's better anyway, since it avoids aggravated violation of DRY by repeating the class name umpteen times. If you want something like this, doyou really have to inherit from Enum?

If I'm saying what you already know I apologize now, but this thread is about what happens when:

class InsertsName(type): @classmethod def prepare(metacls, cls, bases): classdict = {'new_name': lambda: 'haha!'} return classdict

def test(): new_name = 'Jose' # if here will result in str not callable error class SomeClass(metaclass=InsertsName): surprise = new_name() new_name = 'Clara' # if here will result in NameError: free variable...

However, if that class definition is either top level, or if the function itself does not define nor use the 'new_name', there is no problem.

Enum was being used in the example because that's what I was toying with when I found the problem.

-- Ethan

More information about the Python-Dev mailing list