[Python-Dev] class name spaces inside an outer function
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~
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