HistoricalData.retrieve_data throws AttributeError: 'DataFrame' object has no attribute 'append'

[power-edge]

opening PR for fix

[Ahmed-Aziz-Belkahia]

        for i in range(int(request_volume / max_per_mssg) + 1):
            provisional_start = start + timedelta(0, i * (self.granularity * max_per_mssg))
            provisional_start = self._date_cleaner(provisional_start)
            provisional_end = start + timedelta(0, (i + 1) * (self.granularity * max_per_mssg))
            provisional_end = self._date_cleaner(provisional_end)

            print("Provisional Start: {}".format(provisional_start))
            print("Provisional End: {}".format(provisional_end))
            response = requests.get(
                "https://api.pro.coinbase.com/products/{0}/candles?start={1}&end={2}&granularity={3}".format(
                    self.ticker,
                    provisional_start,
                    provisional_end,
                    self.granularity))

            if response.status_code in [200, 201, 202, 203, 204]:
                if self.verbose:
                    print('Data for chunk {} of {} extracted'.format(i+1,
                                                                     (int(request_volume / max_per_mssg) + 1)))
                dataset = pd.DataFrame(json.loads(response.text))
                if not dataset.empty:
                    print("Type of data:", type(data))
                    print("Type of dataset:", type(dataset))
                    print("Dataset content:", dataset)
                    if data.empty:
                        data = dataset
                    else:
                        data = pd.concat([data, dataset], ignore_index=True)
                    time.sleep(randint(0, 2))
                else:
                    print("""CoinBase Pro API did not have available data for '{}' beginning at {}.  
                    Trying a later date:'{}'""".format(self.ticker,
                                                       self.start_date,
                                                       provisional_start))
                    time.sleep(randint(0, 2))
            elif response.status_code in [400, 401, 404]:
                if self.verbose:
                    print(
                        "Status Code: {}, malformed request to the CoinBase Pro API.".format(response.status_code))
                sys.exit()
            elif response.status_code in [403, 500, 501]:
                if self.verbose:
                    print(
                        "Status Code: {}, could not connect to the CoinBase Pro API.".format(response.status_code))
                sys.exit()
            else:
                if self.verbose:
                    print("Status Code: {}, error in connecting to the CoinBase Pro API.".format(
                        response.status_code))
                sys.exit()

                this is the fix