From fdf38d35622c3735e86aa3336e27dc5140786f36 Mon Sep 17 00:00:00 2001
From: Richard Frank <rich@quantopian.com>
Date: Sun, 24 Mar 2013 11:58:03 -0400
Subject: [PATCH] BUG: Moved asserts back to before calculations that rely on
 them.

This means we get a failed assert immediately, instead of an
OverflowError later.
---
 zipline/finance/trading.py | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/zipline/finance/trading.py b/zipline/finance/trading.py
index cf15aa7d..a0ade9cd 100644
--- a/zipline/finance/trading.py
+++ b/zipline/finance/trading.py
@@ -263,6 +263,15 @@ class SimulationParameters(object):
         self.period_start = period_start
         self.period_end = period_end
         self.capital_base = capital_base
+
+        assert self.period_start <= self.period_end, \
+            "Period start falls after period end."
+
+        assert self.period_start <= environment.last_trading_day, \
+            "Period start falls after the last known trading day."
+        assert self.period_end >= environment.first_trading_day, \
+            "Period end falls before the first known trading day."
+
         self.first_open = self.calculate_first_open()
         self.last_close = self.calculate_last_close()
         start_index = \
@@ -274,14 +283,6 @@ class SimulationParameters(object):
         self.trading_days = \
             environment.trading_days[start_index:end_index + 1]
 
-        assert self.period_start <= self.period_end, \
-            "Period start falls after period end."
-
-        assert self.period_start <= environment.last_trading_day, \
-            "Period start falls after the last known trading day."
-        assert self.period_end >= environment.first_trading_day, \
-            "Period end falls before the first known trading day."
-
     def calculate_first_open(self):
         """
         Finds the first trading day on or after self.period_start.