Generators can only yield ints?

[defn noob]

def letters():
        a = xrange(ord('a'), ord('z')+1)
        B = xrange(ord('A'), ord('Z')+1)
        while True:
                yield chr(a)
                yield chr(B)


>>> l = letters()
>>> l.next()

Traceback (most recent call last):
  File "<pyshell#225>", line 1, in <module>
    l.next()
  File "<pyshell#223>", line 5, in letters
    yield chr(a)
TypeError: an integer is required
>>>


Any way to get around this?
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