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tff.framework.transform_postorder

Traverses comp recursively postorder and replaces its constituents.

tff.framework.transform_postorder(
    comp,
    transform
)

Defined in python/core/impl/transformation_utils.py.

For each element of comp viewed as an expression tree, the transformation transform is applied first to building blocks it is parameterized by, then the element itself. The transformation transform should act as an identity function on the kinds of elements (computation building blocks) it does not care to transform. This corresponds to a post-order traversal of the expression tree, i.e., parameters are alwaysd transformed left-to-right (in the order in which they are listed in building block constructors), then the parent is visited and transformed with the already-visited, and possibly transformed arguments in place.

NOTE: In particular, in Call(f,x), both f and x are arguments to Call. Therefore, f is transformed into f', next x into x' and finally, Call(f',x') is transformed at the end.

Args:

  • comp: A computation_building_block.ComputationBuildingBlock to traverse and transform bottom-up.
  • transform: The transformation to apply locally to each building block in comp. It is a Python function that accepts a building block at input, and should return a (building block, bool) tuple as output, where the building block is a computation_building_block.ComputationBuildingBlock representing either the original building block or a transformed building block and the bool is a flag indicating if the building block was modified as.

Returns:

The result of applying transform to parts of comp in a bottom-up fashion, along with a Boolean with the value True if comp was transformed and False if it was not.

Raises:

  • TypeError: If the arguments are of the wrong computation_types.
  • NotImplementedError: If the argument is a kind of computation building block that is currently not recognized.