How would one go about adding animation data (keyframes / FCurves) to an empty object using the Python API?
This is to be able to have full control over creation of keyframes and setting interpolation properties without having to use Object.keyframe_insert, finding the just made keyframe (as the function doesn't return the keyframe), and then adjusting interpolation properties.
Many posts I've seen about adding animation data via the Python API uses the keyframe_insert function of class bpy_struct, as seen here:
# Add keyframe to x axis on frame 1
obj.location.x = 1.23
obj.keyframe_insert(data_path="location", index=0, frame=1)
This Blender StackExchange answer shows how one can access FCurves of an object once they are created. Though, the post does not show how to create a FCurve from scratch.
To access the FCurve(s) that modifies a data_path on the currently selected object, one can do this (as shown in the post):
context = bpy.context
obj = context.object
action = obj.animation_data.action
# All location fcurves on the object
fcurves = [fc for fc in action.fcurves if fc.data_path == "location"]
# Iterate over each axis (of location property)
for fc in fcurves:
# X axis would be axis == 0
axis = fc.array_index
Before running the keyframe_insert function on an empty object, the animation_data property of the Object is NoneType. Running keyframe_insert sets this property to an instance of AnimData somehow. animation_data.action therefore is also non-existent, therefore one cannot begin adding FCurves (if even possible).