Remove TFLowOpName

[brandonwillard]

The TFlowOpName string type was an attempt to "smooth out" some of the name-uniqueness constraints in TF (e.g. so that equality could exist between a meta object with the name "value:0" and a recreated base object with an automatically generated name like "blah/value_1:0"). While sometimes convenient, this isn't the right approach, since it causes problems when the ignored name distinctions are actually intended to correspond to distinct base objects.

[brandonwillard]

Working on this has brought up something that needs addressing: the connection between meta objects and their names is not one-to-one with the TF graphs in which meta objects create their corresponding reified base objects.

For example, consider the following:

import tensorflow as tf

from tensorflow.python.eager.context import graph_mode

from symbolic_pymc.tensorflow.meta import mt, TFlowMetaNodeDef, TFlowMetaOp


with graph_mode(), tf.Graph().as_default() as test_graph:

    add_tf = tf.add(1, 1)

    assert add_tf.name == 'Add:0'

with graph_mode(), test_graph.as_default():

    # This could be a meta version of `add_tf.op.node_def`
    node_def_mt = TFlowMetaNodeDef('Add', 'Add', {})

    assert mt(add_tf.op.node_def) == node_def_mt

    # This could be a meta version of `add_tf.op`
    inputs_mt = mt(add_tf.op.inputs)
    test_op_mt = TFlowMetaOp(mt.Add, node_def_mt, inputs_mt)

    assert mt(add_tf.op) == test_op_mt

In this example, we've created a TF Add node, add_tf, and created—by hand—a meta NodeDef and meta Operation that could be meta versions of add_tf's constituent Operation and NodeDef base objects.

Now, when we reify the meta Operation, test_op_mt, we find that the base object it produces does not correspond exactly to the underlying meta object, because its name values are different.

with graph_mode(), test_graph.as_default():

    test_op_tf = test_op_mt.reify()

    # The reified, base/TF `Operation` object has a different name!
    assert test_op_mt.name != test_op_tf.name

This discrepancy is due to the fact that test_graph already has a node with the name Add (i.e. the original add_tf's Operation).

One solution: we could check for elements with the desired/specified meta object names in the current TF graph and verify that the proposed meta objects are in-line with those—and, say, raise exceptions when they aren't. At the very least, such a process could save some effort (re)constructing TF objects that already exist and/or better imputation of unspecified information in meta objects (e.g. dtypes and shapes).

Also, TFlowMetaNodeDef needs a custom reify method; the base class method currently does not work for this type.