user805627 user805627 - 4 months ago 97
Python Question

How to implement a subscriptable class in Python (subscriptable class, not subscriptable object)?

To implement a subscriptable object is easy, just implement

__getitem__
in this object's class definition.

But now I want to implement a subscriptable class. For example, I want to implement this code:

class Fruit(object):
Apple = 0
Pear = 1
Banana = 2
#________________________________
#/ Some other definitions, \
#\ make class 'Fruit' subscriptable. /
# --------------------------------
# \ ^__^
# \ (oo)\_______
# (__)\ )\/\
# ||----w |
# || ||

print Fruit['Apple'], Fruit['Banana']
#Output: 0 2


I know
getattr
can do the same thing, but I feel subscript accessing is more elegant.

Answer

Seems to work by changing the metaclass. For Python 2:

class GetAttr(type):
    def __getitem__(cls, x):
        return getattr(cls, x)

class Fruit(object):
    __metaclass__ = GetAttr

    Apple = 0
    Pear = 1
    Banana = 2

print Fruit['Apple'], Fruit['Banana']
# output: 0 2

On Python 3, you should use Enum directly:

import enum

class Fruit(enum.Enum):
    Apple = 0
    Pear = 1
    Banana = 2

print(Fruit['Apple'], Fruit['Banana'])
# Output: Fruit.Apple, Fruit.Banana
print(Fruit['Apple'].value, Fruit['Banana'].value)
# Output: 0 2