I did some experimentation and found some inconsistency between int and complex:

>>> int('\xA11')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'utf8' codec can't decode byte 0xa1 in position 0: invalid start byte

but
>>> complex('\xA11')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: complex() arg is a malformed string

The int behavior is probably a bug that should be reported separately.