25.06.17 15:06, lucas via Python-ideas пише:
I often use generators, and itertools.chain on them. What about providing something like the following:a = (n for n in range(2)) b = (n for n in range(2, 4)) tuple(a + b) # -> 0 1 2 3 This, from user point of view, is just as how the __add__ operator works on lists and tuples. Making generators works the same way could be a great way to avoid calls to itertools.chain everywhere, and to limits the differences between generators and other "linear" collections. I do not know exactly how to implement that (i'm not that good at C, nor CPython source itself), but by seeing the sources, i imagine that i could do something like the list_concat function at Objects/listobject.c:473, but in the Objects/genobject.c file, where instead of copying elements i'm creating and initializing a new chainobject as described at Modules/itertoolsmodule.c:1792. (In pure python, the implementation would be something like `def __add__(self, othr): return itertools.chain(self, othr)`)
It would be weird if the addition is only supported for instances of the generator class, but not for other iterators. Why (n for n in range(2)) + (n for n in range(2, 4)) works, but iter(range(2)) + iter(range(2, 4)) and iter([0, 1]) + iter((2, 3)) don't? itertools.chain() supports arbitrary iterators. Therefore you will need to implement the __add__ method for *all* iterators in the world.
However itertools.chain() accepts not just *iterators*. It works with *iterables*. Therefore you will need to implement the __add__ method also for all iterables in the world. But __add__ already is implemented for list and tuple, and many other sequences, and your definition conflicts with this.
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