'ProductDPSpace' object has no attribute 'integrate'

[pelegm]

Should be implemented. So far:

In [2]: import drv.real

In [3]: r = drv.real.FRDRV('r', drv.pspace.FDPSpace(range(10)[::-1]), lambda x: x**2)

In [4]: (r+1).mean

raises

Traceback (most recent call last):
  File "<ipython-input-4-b4acbe6f318b>", line 1, in <module>
    (r+1).mean
  File "drv/real.py", line 62, in mean
    return self.moment(1)
  File "drv/real.py", line 123, in moment
    return self.pspace.integrate(self._moment_func(n))
AttributeError: 'ProductDPSpace' object has no attribute 'integrate'