'Gets the bitlist corresponding to a subset.
Examples
>>> from sympy.combinatorics.subsets import Subset
>>> Subset.bitlist_from_subset([\'c\', \'d\'], [\'a\', \'b\', \'c\', \'d\'])
\'0011\'
See Also
subset_from_bitlist'

@classmethod
def bitlist_from_subset(self, subset, superset):

    bitlist = (['0'] * len(superset))
    if (type(subset) is Subset):
        subset = subset.args[0]
    for i in Subset.subset_indices(subset, superset):
        bitlist[i] = '1'
    return ''.join(bitlist)
