Python iterator as class member?

debugcn Published at Dev

Jiangfan Du

I have a scheme like:

class Base(object):
    param, d=0, 1
    def get_all(self):
        while True:
            a = self.get_xxx(param)
            if not a:
                break
            handle(a)
            param += d

class A(Base):
    def get_xxx(param):
        return some_method(param)

class B(Base):
    def get_xxx(param):
        return other_method(param)

Then, I was informed that for B, after each get_xxx param should be a+1 instead of param+d. That means I need to extract the param change logic at the end of get_all. I came up with a scheme using iterator:

class Base(object):
    def get_all(self):
        get_xxx = self.get_xxx()
        while True:
            a = get_xxx.next()
            if not a:
                break
            handle(a)

class A(Base):
    def get_xxx():
        param, d = 0, 1
        while True:
            yield somemethod(param)
            param += d

class B(Base):
    def get_xxx():
        param = 0
        while True:
            a = somemethod(param)
            param = a + 1
            yield a

Problem solved, but somehow I feel uncomfortable. So I wonder if there's a better solution? Many thanks!

jonrsharpe

I would make things like param and d instance attributes:

class Base(object):
    def __init__(self):
        self.param = 0
        self.d = 1

then you don't have to pass anything explicitly into get_xxx(). You could replace

param += d

with

self.iterate_param(a):

in Base.get_all() then define iterate_param() appropriately in your two subclasses, i.e.

class A(Base):
    ...
    def iterate_param(self, a):
        self.param += self.d

class B(Base):
    ...
    def iterate_param(self, a):
        self.param = a + 1

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