list – How to merge common data of dictionary in python

I have a dictionary with:

mydict = [
           {"product_id": '1', "qty": 2,'req_id':'1'},
           {"product_id": '1', "qty": 3,'req_id':'2'},
           {"product_id": '2', "qty": 4,'req_id':'3'},
           {"product_id": '2', "qty": 5,'req_id':'5'},
           {"product_id": '2', "qty": 5,'req_id':'6'},
           {"product_id": '3', "qty": 5,'req_id':'7'},

And I want to convert it by common product_id. It will sum qty and show the req_id into nested dict. Expected result:

  {"product_id": '1', "qty": 5, reqId:[{'req_id':'1','req_id':'2'}]},
  {"product_id": '2', "qty": 14, reqId:[{'req_id':'3','req_id':'5','req_id':'6'}]},
  {"product_id": '3', "qty": 5, reqId:[{'req_id':'7'}]},

Any help regarding this would be appreciated. Thanks