From 7ae23e23403df5f515230a72b955bd12b0cb3ee8 Mon Sep 17 00:00:00 2001
From: Frederic Fortier <fredfortier@gmail.com>
Date: Thu, 25 Jan 2018 17:40:45 -0500
Subject: [PATCH] BLD: conditionally fetching single or multi tickers for
 performance reasons

---
 catalyst/exchange/ccxt/ccxt_exchange.py | 38 +++++++++++++++++++------
 catalyst/exchange/exchange.py           |  2 +-
 tests/exchange/test_ccxt.py             |  2 +-
 3 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/catalyst/exchange/ccxt/ccxt_exchange.py b/catalyst/exchange/ccxt/ccxt_exchange.py
index 543466aa..3e5d5b29 100644
--- a/catalyst/exchange/ccxt/ccxt_exchange.py
+++ b/catalyst/exchange/ccxt/ccxt_exchange.py
@@ -997,16 +997,36 @@ class CCXT(Exchange):
         list[dict[str, float]
 
         """
-        symbols = self.get_symbols(assets)
-        try:
-            results = self.api.fetch_tickers(symbols=symbols)
-        except (ExchangeError, NetworkError) as e:
-            log.warn(
-                'unable to fetch tickers {} / {}: {}'.format(
-                    self.name, symbols, e
+        if len(assets) == 1:
+            symbol = self.get_symbol(assets[0])
+            try:
+                log.debug('fetching single ticker: {}'.format(symbol))
+                results = dict()
+                results[symbol] = self.api.fetch_ticker(symbol=symbol)
+
+            except (ExchangeError, NetworkError) as e:
+                log.warn(
+                    'unable to fetch ticker {} / {}: {}'.format(
+                        self.name, symbol, e
+                    )
                 )
-            )
-            raise ExchangeRequestError(error=e)
+                raise ExchangeRequestError(error=e)
+
+        elif len(assets) > 1:
+            symbols = self.get_symbols(assets)
+            try:
+                log.debug('fetching multiple tickers: {}'.format(symbols))
+                results = self.api.fetch_tickers(symbols=symbols)
+
+            except (ExchangeError, NetworkError) as e:
+                log.warn(
+                    'unable to fetch tickers {} / {}: {}'.format(
+                        self.name, symbols, e
+                    )
+                )
+                raise ExchangeRequestError(error=e)
+        else:
+            raise ValueError('Cannot request tickers with not assets.')
 
         tickers = dict()
         for asset in assets:
diff --git a/catalyst/exchange/exchange.py b/catalyst/exchange/exchange.py
index c66121bc..1d96d886 100644
--- a/catalyst/exchange/exchange.py
+++ b/catalyst/exchange/exchange.py
@@ -701,7 +701,7 @@ class Exchange:
                     )
 
         positions_value = 0.0
-        if positions is not None:
+        if positions:
             assets = set([position.asset for position in positions])
             tickers = self.tickers(assets)
 
diff --git a/tests/exchange/test_ccxt.py b/tests/exchange/test_ccxt.py
index 3683ca4a..af455cc4 100644
--- a/tests/exchange/test_ccxt.py
+++ b/tests/exchange/test_ccxt.py
@@ -76,7 +76,7 @@ class TestCCXT(BaseExchangeTestCase):
             self.exchange.get_asset('zrx_eth'),
         ]
         tickers = self.exchange.tickers(assets)
-        assert len(tickers) == 1
+        assert len(tickers) == 2
         pass
 
     def test_my_trades(self):