AttributeError: 'frozenset' object has no attribute 'index'

This error occurs when you try to access the index of an element in a frozenset. Frozensets are immutable and unordered, which means they do not support indexing.

To fix this error, you can convert the frozenset to a list or tuple, which are ordered and support indexing. Then, you can access the index of an element in the list or tuple.

Example:

fset = frozenset([1, 2, 3])
# fset.index(2)  # This will raise AttributeError

# Convert frozenset to list and access index
lst = list(fset)
print(lst.index(2))  # Output: 1

In the above example, we first created a frozenset `fset` and tried to access the index of element `2` using `fset.index(2)`. This raised an AttributeError. Then, we converted the frozenset to a list `lst` using `list(fset)` and accessed the index of element `2` using `lst.index(2)`, which returned the correct index `1`.