Dag with multiple copies of a funcnode

[cavart28]

In some cases, the user may want to re-use a given function several times within a single dag. Since the name of the function acts as an id for it, that name needs to be changed when created the corresponding funcnode (using the "name" parameter).

This is not the most natural since the function does not change, so why would we require the user to "rename" it (assuming that their inputs/outputs are bound correctly at least)?

In fact the name parameter was intended to be used as an id rather than its name, and is a bit of a misnomer in that respect. There is another parameter of funcnode, namely "label", which allows to control the printed name of the node when using the digraph method. Thanks to that parameter, there is no loss of functionality overall for a user aware of this subtlety but perhaps a bit of confusion since the abstract functionality of a "name" is actually shared by those two parameters.

The actual behavior of a dag with several funcnodes sharing the same name is not clear either. For now the simplest solution is to warn the user when they attempt to create a dag with "repeated" funcnodes (i.e. funcnodes with the same name). Then later also understanding the actual side effects of having two funcnodes and possibly modifying the behavior of a dag in that case.

[cavart28]

Here is an interesting behavior. The same functions is used twice in a dag, with the same name. The dag runs but the digraph cannot be plotted:

def f(x):
    return x

def g(y):
    return y

def times_two(a):
    return 2 * a

f_node = FuncNode(func=f,
                  name='f',
                  bind={'x': 'x'},
                  out='fx')

g_node = FuncNode(func=g,
                  name='g',
                  bind={'y': 'y'},
                  out='gy')

f_times_two_node = FuncNode(func=times_two,
                            name='times_two',
                            bind={'a': 'fx'},
                            out='two_fx')

g_times_two_node = FuncNode(func=times_two,
                            name='times_two',
                            bind={'a': 'gy'},
                            out='two_gy')

d = DAG([f_node, g_node, f_times_two_node, g_times_two_node])

d.dot_digraph()

[cavart28]

The issue is fixed since it is now NOT possible anymore to use the same function name twice for two different nodes (an error is raised).

[cavart28]

I take that back, the issue is still alive. One can still make a dag with two funcnodes created with the same function. And as before, though the dag can be created and used, the plotting function fails. One quick way to fix the problem would be the force the user to use different function names for all the nodes, even if one is a copy of another. See the example above, with and without the plotting.