Why Do Tuples In Python Work With Reversed But Do Not Have __reversed__?

In discussion of this answer we realized that tuples do not have a __reversed__ method. My guess was that creating the iterator would require mutating the tuple. And yet tuples pla

Solution 1:

According to the spec:

reversed(seq)

Return a reverse iterator. seq must be an object which has a reversed() method or supports the sequence protocol (the __len__() method and the __getitem__() method with integer arguments starting at 0).

Solution 2:

EDIT: well, I try to say it again (english is not my native language) - with example.

Some functions - I call them fun(object) - can use object.__func__() to do the job or they use other functions in object if there is no object.__func__()

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For example str() - when you use str(object) it calls object.__str__(), but if there is no object.__str__() then it calls object.__repr__().

So you can use str() with object which has no __str__() and still get some result.

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Other example < - when you use a < b it tries to use a.__lt__() but if there is no a.__lt__() it tries to use a.__gt__() (and maybe other functions too)

classMyClass():

    def__str__(self):
        return"MyClass: __str__"def__repr__(self):
        return"MyClass: __repl__"#-------------------------def__lt__(self, other):
        returnTruedef__gt__(self, other):
        returnTrue#-------------------------

a = MyClass()
b = MyClass()

print( str(a) )

print( a < b )

1. You can remove __str__ to get different result.

2. You can change True/False in __lt__ and you can see that result is changed. Then you can remove __lt__ and you can change True/False in __gt__ and you see that result is changed again.