On Sun, Aug 26, 2018, 9:24 PM James Lu <jam...@gmail.com> wrote: > Hi Johnathan > > I echo your points. Indeed, the PEP referenced to refers to a "tuple > expression" in the grammatical and not the programmatic sense. > > Finally, here's something that surprised me a little bit > > >>> x = [1, 2]; id(x) > 140161160364616 > >>> x += [3, 4]; id(x) > 140161160364616 > > >>> x = (1, 2); id(x) > 140161159928520 > >>> x += (3, 4); id(x) > 140161225906440 > > Notice that '+=' creates uses the same object when the object is > a > list, but creates a new object. This raises the question: Why and > how > does Python behave in this way? > > It's because lists are mutable are tuples are immutable. > There's a dunder iadd method and a dunder add method. > iadd magic methods, operating on the left hand side, return None and > modify the object in-place. add magic methods return the result and > don't modify the object it's called on. > iadd is mutable add, whereas add is "return a copy with the result > added" > > >>> tuple.__iadd__ > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > AttributeError: type object 'tuple' has no attribute '__iadd__' > type object 'tuple' has no attribute '__iadd__' > >>> tuple.__add__ > <slot wrapper '__add__' of 'tuple' objects> > >>> list.__iadd__ > <slot wrapper '__iadd__' of 'list' objects> > >>> list.__add__ > <slot wrapper '__add__' of 'list' objects> > > > tuple1 = tuple1.__add__(tuple2) > > list1.__iadd__(list2) > > > Does it IN PRACTICE bring sufficient benefits to users? > > I found myself needing this when I was writing a monte-carlo > simulation in python that required incrementing a tallying counter > from a subroutine. >
Wouldn't a numpy array be very suited for this kind of task? >
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