Watch out for the return value of __len__

When I overridden __len__ in my class and called it, the following error occurred.

OverflowError: cannot fit 'int' into an index-sized integer

The cause was in the __len__ specification. Apparently, the return value of __len__ must meet the following conditions.

--Integer type (int) --0 or more --Below and below the upper limit of signed 32-bit integers (0x7FFFFFFF) --The "signed 32-bit integer" part may differ depending on the environment.


class ReturnStr(object):
    def __len__(self): return "abc"

class ReturnFloat(object):
    def __len__(self): return 1.0

class ReturnNegativeNumber(object):
    def __len__(self): return -1

class ReturnBigNumber(object):
    def __len__(self): return 0x7FFFFFFF + 1

class ReturnSmallNumber(object):
    def __len__(self): return 0x7FFFFFFF

if __name__ == "__main__":
    len(ReturnStr())            #=> TypeError: 'str' object cannot be interpreted as an integer
    len(ReturnFloat())          #=> TypeError: 'float' object cannot be interpreted as an integer
    len(ReturnNegativeNumber()) #=> ValueError: __len__() should return >= 0
    len(ReturnBigNumber())      #=> OverflowError: cannot fit 'int' into an index-sized integer
    len(ReturnSmallNumber())    #=> OK

In my case, it seems that it was an exception because the return value of __len__ was too large (´ ・ ω ・`)

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