Reply To: Keyframes fast selection

[Dwayne Savage]

***Edit*** Forgot to mention I added to the select menu on the dopesheet editor.

Well, that was surprisingly easy. I just added an append to the register and a remove in the unregister.

bpy.types.DOPESHEET_MT_select.append(menu_func)
bpy.types.DOPESHEET_MT_select.remove(menu_func)

So the whole script is:

bl_info = {
    "name": "Partial Deselect",
    "blender": (3, 0, 0),
    "category": "Object",
}

import bpy

def main(context, nthkey=2):
        for action in bpy.data.actions:
            for channel in action.fcurves:
                for key in channel.keyframe_points.values()[0::nthkey]:
                    key.select_control_point = False
                    key.select_left_handle = False
                    key.select_right_handle = False

class ChannelSelect4Key(bpy.types.Operator):
    """Partial deSelect"""      # Use this as a tooltip for menu items and buttons.
    bl_idname = "anim.channel_select_4th"
    bl_label = "DeSelect 1 keyframe every 4 keys"
    bl_options = {'REGISTER', 'UNDO'}  # Enable undo for the operator.
    def execute(self, context):
        main(context, 4)
        return {'FINISHED'}

class ChannelSelect3Key(bpy.types.Operator):
    """Partial deSelect"""      # Use this as a tooltip for menu items and buttons.
    bl_idname = "anim.channel_select_3th"
    bl_label = "DeSelect 1 keyframe every 3 keys"
    bl_options = {'REGISTER', 'UNDO'}  # Enable undo for the operator.
    def execute(self, context):
        main(context, 3)
        return {'FINISHED'}

class ChannelSelect2Key(bpy.types.Operator):
    '''Select odd keys for selected channels in the dopesheet'''
    bl_idname = "anim.channel_select_2nd"
    bl_label = "DeSelect 1 keyframe every 2 keys (even)"
    bl_options = {'REGISTER', 'UNDO'}  # Enable undo for the operator.
    def execute(self, context):
        main(context, 2)
        return {'FINISHED'}

def menu_func(self, context):
    self.layout.operator(ChannelSelect4Key.bl_idname)
    self.layout.operator(ChannelSelect3Key.bl_idname)
    self.layout.operator(ChannelSelect2Key.bl_idname)

def register():
    bpy.utils.register_class(ChannelSelect4Key)
    bpy.utils.register_class(ChannelSelect3Key)
    bpy.utils.register_class(ChannelSelect2Key)
    bpy.types.DOPESHEET_MT_select.append(menu_func)

def unregister():
    bpy.utils.unregister_class(ChannelSelect4Key)
    bpy.utils.unregister_class(ChannelSelect3Key)
    bpy.utils.unregister_class(ChannelSelect2Key)
    bpy.types.DOPESHEET_MT_select.remove(menu_func)

if __name__ == "__main__":
    register()

Or you can download and install as an addon.

https://drive.google.com/drive/folders/0B5x4OjbuDbY5fmxRWXprNTItWEVFMmhhTFRCSkFlZ2RuS2YwcW4wMHhQQW04ekdPV25aVms?resourcekey=0-PQxdYmfIoaVYZ96YbJtmnw&usp=sharing