This is the environment implementation of :meth:`BaseKerning.interpolate`.

        * **factor** will be an :ref:`type-int-float`, ``tuple`` or ``list``.
        * **minKerning** will be a :class:`BaseKerning` object.
        * **maxKerning** will be a :class:`BaseKerning` object.
        * **round** will be a ``bool`` indicating if the interpolated kerning
          should be rounded.
        * **suppressError** will be a ``bool`` indicating if incompatible data
          should be ignored.

        Subclasses may override this method.

def _interpolate(self, factor, minKerning, maxKerning,
                     round=True, suppressError=True):
        """
        This is the environment implementation of :meth:`BaseKerning.interpolate`.

        * **factor** will be an :ref:`type-int-float`, ``tuple`` or ``list``.
        * **minKerning** will be a :class:`BaseKerning` object.
        * **maxKerning** will be a :class:`BaseKerning` object.
        * **round** will be a ``bool`` indicating if the interpolated kerning
          should be rounded.
        * **suppressError** will be a ``bool`` indicating if incompatible data
          should be ignored.

        Subclasses may override this method.
        """
        import fontMath
        kerningGroupCompatibility = self._testKerningGroupCompatibility(
                                                        minKerning,
                                                        maxKerning,
                                                        suppressError=suppressError
                                                        )
        if not kerningGroupCompatibility:
            self.clear()
        else:
            minKerning = fontMath.MathKerning(
                kerning=minKerning, groups=minKerning.font.groups)
            maxKerning = fontMath.MathKerning(
                kerning=maxKerning, groups=maxKerning.font.groups)
            result = interpolate(minKerning, maxKerning, factor)
            if round:
                result.round()
            self.clear()
            result.extractKerning(self.font)