generator keeps returning the same value

问题:

I am stuck on this one piece of code because I can't get the generator to return me a the next value every time its called – it just stays on the first one! Take a look:

from numpy import *

def ArrayCoords(x,y,RowCount=0,ColumnCount=0):   # I am trying to get it to print
    while RowCount<x:                            # a new coordinate of a matrix
        while ColumnCount<y:                     # left to right up to down each
            yield (RowCount,ColumnCount)         # time it's called.
            ColumnCount+=1
        RowCount+=1
        ColumnCount=0

Here is what I get:

>>> next(ArrayCoords(20,20))
... (0, 0)
>>> next(ArrayCoords(20,20))
... (0, 0)

But it's just stuck on the first one! I expected this:

>>> next(ArrayCoords(20,20))
... (0, 0)
>>> next(ArrayCoords(20,20))
... (0, 1)
>>> next(ArrayCoords(20,20))
... (0, 2)

Could you guys help me out with the code as well as explain why it is so? Thank you in advance!

回答1:

Each time you call ArrayCoords(20,20) it returns a new generator object, different to the generator objects returned every other time you call ArrayCoords(20,20). To get the behaviour you want, you need to save the generator:

>>> coords = ArrayCoords(20,20)
>>> next(coords)
(0, 0)
>>> next(coords)
(0, 1)
>>> next(coords)
(0, 2)

回答2:

You create a new generator on every line. Try this instead:

iterator = ArrayCoords(20, 20)
next(iterator)
next(iterator)