how to count the total number of documents after pymongo aggregation query?

related codes

match1 = {"$match": {"regDate": {"$gte": datetime(2018, 6, 1), "$lt": datetime(2018, 6, 30)}}}
lookup = {"$lookup":
              {
                  "from": "recharge",
                  "localField": "_id",
                  "foreignField": "uid",
                  "as": "recharge"
              }
          }
project = {"$project":
               {
                   "_id": 1,
                   "regDate": 1,
                   "recharge.from": 1,
                   "recharge.rechargeDate": 1,
               }
        }
match2 = {"$match": {"recharge.from": "weixin"}}
match3 = {"$match": {"recharge.from": "alipay"}}
match4 = {"$match": {"recharge.rechargeDate": {"$gte": datetime(2018, 6, 1), "$lt": datetime(2018, 6, 30)}}}
pipeline = [match1, lookup, project, match2, match3, match4]
result = collection.aggregate(pipeline)

for i in result:
    pprint.pprint(i)

part of the result information is as follows:

{"_id": ObjectId("5b1359c11a6206742ffc3848"),
 "recharge": [{"from": "regCoupon",
               "rechargeDate": datetime.datetime(2018, 6, 3, 3, 13, 33, 591000)},
              {"from": "alipay"},
              {"from": "weixin",
               "rechargeDate": datetime.datetime(2018, 6, 3, 3, 14, 32, 525000)}],
 "regDate": datetime.datetime(2018, 6, 3, 3, 0, 17, 300000)}
{"_id": ObjectId("5b13bc0e1a6206742ffc3960"),
 "recharge": [{"from": "regCoupon",
               "rechargeDate": datetime.datetime(2018, 6, 3, 9, 59, 55, 503000)},
              {"from": "alipay"},
              {"from": "weixin",
               "rechargeDate": datetime.datetime(2018, 6, 3, 14, 43, 16, 430000)},
              {"from": "weixin",
               "rechargeDate": datetime.datetime(2018, 6, 10, 11, 3, 18, 861000)}],
 "regDate": datetime.datetime(2018, 6, 3, 9, 59, 42, 470000)}
{"_id": ObjectId("5b1419181a6206742ffc3a2d"),
 "recharge": [{"from": "regCoupon",
               "rechargeDate": datetime.datetime(2018, 6, 3, 16, 36, 46, 138000)},
              {"from": "weixin",
               "rechargeDate": datetime.datetime(2018, 6, 3, 19, 13, 30, 810000)},
              {"from": "weixin",
               "rechargeDate": datetime.datetime(2018, 6, 3, 20, 24, 3, 236000)},
              {"from": "weixin",
               "rechargeDate": datetime.datetime(2018, 6, 4, 1, 48, 56, 870000)},
              {"from": "alipay"},
              {"from": "weixin",
               "rechargeDate": datetime.datetime(2018, 7, 10, 2, 59, 1, 594000)},
              {"from": "weixin",
               "rechargeDate": datetime.datetime(2018, 7, 21, 6, 33, 31, 558000)}],
 "regDate": datetime.datetime(2018, 6, 3, 16, 36, 40, 934000)}

1. list items can print out all filtered lists. What is the total? What should I set with $group id?
2. in the above results, from has regCoupon, besides weixin and alipay. How is Filter?
3. rechargeDate also shows the top-up date in July in the above results. How about Filter?