For now bool() raises OverflowError if __bool__ is not defined and __len__ returns large value.

>>> class A:
...     def __len__(self):
...         return 1 << 1000
... 
>>> bool(A())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: cannot fit 'int' into an index-sized integer
>>> bool(range(1<<1000))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: Python int too large to convert to C ssize_t

Proposed patch makes bool() returning True if len() raises OverflowError.

This is an alternate solution of issue28876.