Trades in fetch_trades should have unified order ASC or DESC

Some exchanges (for example poloniex) returns trades history in the descending order and some others in ascending.

• Programming Language: Python
• CCXT version: 1.10.389
• Exchange: binance, poloniex
• Method: fetch_trades

# example 1: ordered by time desc
ccxt.poloniex ({'verbose': True}).fetch_trades(
                            market['symbol'], # symbol returned by fetch_markets()
                            since=timestamp
                        )

# https://poloniex.com/public?command=returnTradeHistory&currencyPair=BTC_NXT&start=1410158341&end=1410499372

# example 2: ordered by time asc
ccxt.binance ({'verbose': True}).fetch_trades(
                            market['symbol'], # symbol returned by fetch_markets()
                            since=timestamp
                        )
# https://api.binance.com/api/v1/aggTrades?symbol=ETHBTC

I think there should be one unified order (ASC as for me).

This issue can be solved by checking first and last trade’s timestamps and applying reversed iterator if needed.

Posting it because it took me some time to go there and as for me, this behavior is unexpected.

[hippylover]

okok.

[ksanderer]

1. Question: Some exchanges have limitation on max since time. For example, when trying to iterate over exchanges list poloniex will return an undocumented error (can’t return more than 1 month trade history). I think there should be an error or auto adjusting since parameter to maximal available.

2. fetch_trades reversed order (we already discussed earlier). Python reversed return an iterator that hasn’t __getitem__ (so you can’t retrieve order by id) and its type differs from normal behavior (list) so I think it’s a bad idea to return implicitly reversed orders iterator.

Now my code looks like this:

class Reversed:
    def __init__(self, seq):
        self.seq = seq
    def __len__(self):
        return len(self.seq)
    def __getitem__(self, i):
        return self.seq[-(i + 1)]

trades = ccxt.poloniex ().fetch_trades(market['symbol'], since=timestamp)

if trades[0]['timestamp'] > trades[-1]['timestamp']:
    trades = Reversed(trades)

# For some exchanges `type(trades) == list` and for others `type(trades) == Reverses`

Maybe we should explicitly return is_reversed to force reaction from developer? Like this:

trades, is_reversed = ccxt.poloniex ().fetch_trades(market['symbol'], since=timestamp)

if is_reversed:
    # do something with it
    # for example 
    # trades = Reversed(trades)