really_in.py

def really_in(y, xs):
    if y is not True and y is not False:
        '''thanks http://www.reddit.com/r/Python/comments/asmwr/python_boolean_coercion_gotchas/c0j7cd7?context=3'''
        return y in xs
    
    for x in xs:
        if y is x: return True
    return False

True in [1, 2, 3]                   # -> True
really_in(True, [1, 2, 3])          # -> False
really_in(True, [1, 2, True, 3])    # -> True

False in [0, 6, 7]                  # -> True
really_in(False, [0, 6, 7])         # -> False
really_in(False, [0, False, 6, 7])  # -> True
really_in(3, [1,2,3])               # -> True

# The downside of using `really_in' instead of `in' is the loss of the ability to
# override `__eq__' to redefine the behavior of `==' and `in'.