How to read and print data from a dictionary using a modal operator?

Question

The following code creates a dictionary and prints it at regular intervals:

import bpy
import json

class ModalTimerOperator(bpy.types.Operator):
    """Operator which runs its self from a timer"""
    bl_idname = "wm.modal_timer_operator"
    bl_label = "Modal Timer Operator"

    _timer = None

    def modal(self, context, event):
        if event.type in {'RIGHTMOUSE', 'ESC'}:
            self.cancel(context)
            return {'CANCELLED'}

        if event.type == 'TIMER':
            dict = {"a":4}

            msg = 'testDict = '+json.dumps(dict)+'\n'
            msg += 'list = ["a","b","c"]\n'

            msg += 'def printTestFunc(num1,num2):\n'
            msg += '    print(num1)\n'
            msg += '    print(num2)\n'

            msg += 'for i in range(5):\n'
            msg += '    [printTestFunc(0,testDict[key]) for key in list if key in testDict]\n'
            exec(msg)

        return {'PASS_THROUGH'}

    def execute(self, context):
        wm = context.window_manager
        self._timer = wm.event_timer_add(0.1, window=context.window)
        wm.modal_handler_add(self)
        return {'RUNNING_MODAL'}

    def cancel(self, context):
        wm = context.window_manager
        wm.event_timer_remove(self._timer)


def register():
    bpy.utils.register_class(ModalTimerOperator)


def unregister():
    bpy.utils.unregister_class(ModalTimerOperator)


if __name__ == "__main__":
    register()

    # test call
    bpy.ops.wm.modal_timer_operator()

Unfortunately, it returns the following error:

line 28, in modal File "", line 7, in File "", line 7, in NameError: name 'testDict' is not defined

However, when I write the following code using Python without using Blender's ModalOperator there is no error:

import json

dict = {"a":4}

msg = 'testDict = '+json.dumps(dict)+'\n'
msg += 'list = ["a","b","c"]\n'

msg += 'def printTestFunc(num1,num2):\n'
msg += '    print(num1)\n'
msg += '    print(num2)\n'

msg += 'for i in range(5):\n'
msg += '    [printTestFunc(0,testDict[key]) for key in list if key in testDict]\n'
exec(msg)

I think this is a Modal Operator specific trouble. Why does this happen?

Answer 1

Pass a globals dict to exec

Not sure of the reason why it doesn't work.. only have some inklings.

However can populate a dictionary and pass as globals to the exec function.

        if event.type == 'TIMER':
            mydict = {"a":4}
            myglobals = {"testDict": eval(json.dumps(mydict)),
                       "mylist": ["a","b","c"] }

            msg = 'def printTestFunc(num1,num2):\n'
            msg += '    print(num1)\n'
            msg += '    print(num2)\n'

            msg += 'for i in range(5):\n'
            msg += '    [printTestFunc(0,testDict[key]) for key in mylist if key in testDict]\n'
            exec(msg, myglobals, None)

        return {'PASS_THROUGH'}

Alternatively could define vars in the method and pass locals() which will include self, context and event

Note: Good idea not to use builtins like list and dict for variable names. EDIT: Oops did just that with globals