Blender quaternion to euler conversion functions

euler_to_quat.py

import bpy


def quaternion_euler_all_bones(mode, start, end, on_obj):
    for f in range(frame_start, frame_end +1): # Go from start to End
        # for each rig bone in current frame
        for bone in obj.pose.bones:
            #don't forget to restore bone rotation mode for next keyframe
            if mode == "EtoQ":
                bone.rotation_mode = "XYZ"
            elif mode == "QtoE":
                bone.rotation_mode = "QUATERNION"
            
            bpy.context.scene.frame_set(f) # switch to frame position
            
            for fc in obj.animation_data.action.fcurves: #obj.animation_data.action.fcurves - current action curves
                # https://devtalk.blender.org/t/fastest-way-to-get-fcurves-from-bone/11382/2
                if fc.data_path.split('"')[1] == bone.name: #check if current curve represents selected bone
                    
                    for keyframe in fc.keyframe_points: #each keyframe. keyframe.co - struct out of 2 fields [x,y] that represent keyframe position in curves. Where X is time 
                        if(keyframe.co.x == f): #check if bone keyframe time mets with the currently processing keyframe. If so that means that bone has keyframe in this position and because of taht we now can convert it's rotation                            
                            if mode == "EtoQ":
                                bone.rotation_mode = "QUATERNION"
                                bone.keyframe_insert(data_path="rotation_quaternion")
                            elif mode == "QtoE":
                                bone.rotation_mode = "XYZ"
                                bone.keyframe_insert(data_path="rotation_euler")
                            else:
                                continue
                            
def quaternion_euler_selected_bone(mode, start, end, on_obj):

    #bpy.context.object.data.bones.active - selected bone
    #bpy.context.active_pose_bone - selected Pose bone.... well did not expected that there is difference between them...
    bone = bpy.context.active_pose_bone
    for f in range(frame_start, frame_end +1): # Go from start to End
        #don't forget to restore bone rotation mode for next keyframe
        if mode == "EtoQ":
            bone.rotation_mode = "XYZ"
        elif mode == "QtoE":
            bone.rotation_mode = "QUATERNION"
            
        bpy.context.scene.frame_set(f) # switch to frame position
             
        for fc in obj.animation_data.action.fcurves: #obj.animation_data.action.fcurves - current action curves
            # https://devtalk.blender.org/t/fastest-way-to-get-fcurves-from-bone/11382/2
            
            if fc.data_path.split('"')[1] == bone.name: #check if current curve represents selected bone
                
                for keyframe in fc.keyframe_points: #each keyframe. keyframe.co - struct out of 2 fields [x,y] that represent keyframe position in curves. Where X is time 
                    if(keyframe.co.x == f): #check if bone keyframe time mets with the currently processing keyframe. If so that means that bone has keyframe in this position and because of taht we now can convert it's rotation                            
                        if mode == "EtoQ":
                            bone.rotation_mode = "QUATERNION"
                            bone.keyframe_insert(data_path="rotation_quaternion")
                        elif mode == "QtoE":
                            bone.rotation_mode = "XYZ"
                            bone.keyframe_insert(data_path="rotation_euler")
                        else:
                            continue

scn = bpy.context.scene
obj = bpy.context.active_object
frame_start = 1
frame_end = 120
print("-------")
#mode selection
#mode = "QtoE"
mode = "EtoQ"

quaternion_euler_selected_bone(mode, frame_start, frame_end, obj)
#quaternion_euler_all_bones(mode, frame_start, frame_end, obj)