[Python] How to return a response in callback function with flask

here is a dll, that can compare face distance, and the compareFace.dll, I need use callback to receive it's value

now, I want use flask to wrapper it, then can visit by http and json

lib= c.CDLL('comparedFace.dll')
CALLBACKFUNC = c.CFUNCTYPE(None, c.c_int, c.c_char_p)
lib.startComparedFace.restype = c.c_int
lib.startComparedFace.argtypes = (c.c_char_p, c.c_char_p, CALLBACKFUNC)


@app.route('/compare', methods=['GET', 'POST'])
def test():
if request.method == 'POST':

request_json = request.get_json()
print(request_json)
number = request_json.get('number')
image01 = request_json.get('image01')
image02 = request_json.get('image02')
print(image01)
print(image02)


@c.CFUNCTYPE(None, c.c_int, c.c_char_p)
@copy_current_request_context
def callback(status, result_string):

result_json = json.loads(result_string)
distance = result_json['compareResult']

resp_data = {
"number": number,
"distance": distance,
}
print(resp_data)
response = Response(
response=json.dumps(resp_data),
status=200,
mimetype='application/json'
)
return response


lib.startComparedFace(b'd:/1.jpg', b'd:/2.jpg', callback)


run the code, and I receive a error ValueError: View function did not return a response

I know, I should write a return 'xxx' as response

But, I want wait the callback function, and return response in the callback function, so how should I modify my code, thank you.

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