How to determine whether the FCurve array_index is targetting a specific property?

Question

This question is within the context of Geometry Node and drivers.

Using the Python API, we can retrieve the drivers associated to Geometry Nodes of a given node tree this way:

fcurves = tree.animation_data.drivers.values()
for fc in fcurves:
    print("fc data_path: " + fc.data_path + "   array_index=" + str(fc.array_index))

For a node with compound components (vector) such as this one:

we will have the following result:

fc data_path: nodes["Switch.001"].inputs[2].default_value   array_index=0
fc data_path: nodes["Switch.001"].inputs[2].default_value   array_index=1

To get the path of the property, we need to append the array index to the data path, for example: nodes["Switch.001"].inputs[2].default_value[0]

For a node with non-compound component such as this one:

we will have the following result:

fc data_path: nodes["Switch"].inputs[1].default_value   array_index=0

The problem is that the FCurve's array_index mentions 0 even though the property is not compound. So based on this information alone, we cannot determine the right path of the property: it may be either

nodes["Switch"].inputs[1].default_value[0]

or

nodes["Switch"].inputs[1].default_value

If array_index was set to -1 in the case of non-compound property, that would be unambiguous, but as it is 0 we cannot know with this information alone. Hence my question: how can we determine the right data_path of the property in such a case?

Note: a workaround is to access the node property input given the FCurve data_path and check its type dynamically. However this is cumbersome so I was looking for a cleaner way.

Answer 1

A function to check driver fcurve allows array_index > 0

import bpy

def is_array_fcurve(datablock, fc):
    try:
        v = eval(f"datablock.{fc.data_path}")
    except:
        return None # invalid datapath
    return hasattr(v, "__len__") # skip the str case since str can't add driver


# Exmaple:
ob = bpy.context.object

ob.driver_add("location")

fc = ob.animation_data.drivers.find("location")

is_array = is_array_fcurve(ob, fc)
if is_array is True:
    print("array")
elif is_array is False:
    print("not array")