迭代（yield）一个列表

Question

I'm trying to make a method that iterates over a list and returns the next element.

That's my list:

[2, 5, 7, 10, 25, 30, 50, 70]

That's the method I'm working on:

    def iterDenominations(self):
        it = iter(self.listDenominations)
        yield it.__next__()

When I call the method and print the result

firstCall = C.iterDenominations()
print(firstCall)
secondCall = C.iterDenominations()
print(secondCall)

, the first two prints are:

<generator object Currency.iterDenominations at 0x000001D413F6DC10>

<generator object Currency.iterDenominations at 0x000001D4140E2EB0>

What should I do to print '2', '5', '7', ...? Thanks you

Answer 1

yield always creates a new generator. iterDenominations doesn't return the next/first element of self.listDenominations ; it returns a generate that will yield that single element.

If you want to create your own iterator, you can do it the long with with

def iterDenominations(self):
    it = iter(self.listDenominations)
    for x in it:
        yield x

the shorter way

def iterDenominations(self):
    for x in self.listDenominations:
        yield x

or an even shorter way:

def iterDenominations(self):
    yield from self.listDenominations

or the shortest way

def iterDenominations(self):
    return iter(self.listDenominations)

(OK, that's actually two characters longer. But it might look more familiar.)

Answer 2

For that to work, you need to store the state somewhere and then a custom function is a difficult start. I believe you want to use the iterator as it is:

it = iter(my_list)
print(next(it))
print(next(it))