Can I express this as a generator / coroutine?

Suppose I have the following class:

class MyGen(object):
  def next(self):
    return X()

  def send(self, x):
    return f(x)

Is it possible to express it as a single function, using the yield keyword? Suppose I have g = MyGen(). Note that g.next() shouldn't call f(), and g.send(x) shouldn't call X(), b开发者_Python百科ut f() and X() could share some code.

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This code will be almost equivalent:

def my_gen(x=None):
    while True:
        if x is None:
            x = yield X()
        else:
            x = yield f(x)

One difference is that you can't send a value (other than None) to a generator before calling next() for the first time. Another difference is that sending None won't trigger calling f(), since the generator can't distinguish send(None) and next().

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Sven's formulation is exactly the way to go, I just wanted to add that if you want to know more about generators, coroutines and such in Python, this site is the place to go.