Accessing class variables from a list comprehension in the class definition

Question

How do you access other class variables from a list comprehension within the class definition? The following works in Python 2 but fails in Python 3:

class          


        

Answer 1

Since the outermost iterator is evaluated in the surrounding scope we can use zip together with itertools.repeat to carry the dependencies over to the comprehension's scope:

import itertools as it

class Foo:
    x = 5
    y = [j for i, j in zip(range(3), it.repeat(x))]

One can also use nested for loops in the comprehension and include the dependencies in the outermost iterable:

class Foo:
    x = 5
    y = [j for j in (x,) for i in range(3)]

For the specific example of the OP:

from collections import namedtuple
import itertools as it

class StateDatabase:
    State = namedtuple('State', ['name', 'capital'])
    db = [State(*args) for State, args in zip(it.repeat(State), [
        ['Alabama', 'Montgomery'],
        ['Alaska', 'Juneau'],
        # ...
    ])]