BUG: Don't fail on integral floats in event rules.

Coerce and warn instead.

tests/events/test_events.py

@@ -16,12 +16,14 @@ import datetime
 from inspect import isabstract
 import random
 from unittest import TestCase
+import warnings
 
 from nose_parameterized import parameterized
 import pandas as pd
 from six import iteritems
 from six.moves import range, map
 
+from zipline.testing import parameter_space
 import zipline.utils.events
 from zipline.utils.calendars import get_calendar
 from zipline.utils.events import (
@@ -439,6 +441,26 @@ class StatelessRulesTests(RuleTestCase):
             self.assertIs(composed.second, rule2)
             self.assertFalse(any(map(should_trigger, minute)))
 
+    @parameterized.expand([
+        ('month_start', NthTradingDayOfMonth),
+        ('month_end', NDaysBeforeLastTradingDayOfMonth),
+        ('week_start', NthTradingDayOfWeek),
+        ('week_end', NthTradingDayOfWeek),
+    ])
+    def test_pass_float_to_day_of_period_rule(self, name, rule_type):
+        with warnings.catch_warnings(record=True) as raised_warnings:
+            warnings.simplefilter('always')
+            rule_type(n=3)    # Shouldn't trigger a warning.
+            rule_type(n=3.0)  # Should trigger a warning about float coercion.
+
+        self.assertEqual(len(raised_warnings), 1)
+        warning_str = raised_warnings[0].message.message
+
+        # We only implicitly convert from float to int when there's no loss of
+        # precision.
+        with self.assertRaises(TypeError):
+            rule_type(3.1)
+
 
 class StatefulRulesTests(RuleTestCase):
     CALENDAR_STRING = "NYSE"

zipline/utils/events.py

@@ -15,13 +15,17 @@
 from abc import ABCMeta, abstractmethod
 from collections import namedtuple
 import six
+import warnings
 
 import datetime
 import numpy as np
 import pandas as pd
 import pytz
+from toolz import curry
 
+from zipline.utils.input_validation import preprocess
 from zipline.utils.memoize import lazyval
+
 from .context_tricks import nop_context
 
 
@@ -148,6 +152,31 @@ def _build_time(time, kwargs):
         return datetime.time(**kwargs)
 
 
+@curry
+def lossless_float_to_int(funcname, func, argname, arg):
+    """
+    A preprocessor that coerces integral floats to ints.
+
+    Receipt of non-integral floats raises a TypeError.
+    """
+    if not isinstance(arg, float):
+        return arg
+
+    arg_as_int = int(arg)
+    if arg == arg_as_int:
+        warnings.warn(
+            "{f} expected an int for argument {name!r}, but got float {arg}."
+            " Coercing to int.".format(
+                f=funcname,
+                name=argname,
+                arg=arg,
+            ),
+        )
+        return arg_as_int
+
+    raise TypeError(arg)
+
+
 class EventManager(object):
     """Manages a list of Event objects.
     This manages the logic for checking the rules and dispatching to the
@@ -402,8 +431,10 @@ class NotHalfDay(StatelessRule):
 
 
 class TradingDayOfWeekRule(six.with_metaclass(ABCMeta, StatelessRule)):
+    @preprocess(n=lossless_float_to_int('TradingDayOfWeekRule'))
     def __init__(self, n, invert):
         if not 0 <= n < MAX_WEEK_RANGE:
+            import nose.tools; nose.tools.set_trace()
             raise _out_of_range_error(MAX_WEEK_RANGE)
 
         self.td_delta = (-n - 1) if invert else n
@@ -443,6 +474,8 @@ class NDaysBeforeLastTradingDayOfWeek(TradingDayOfWeekRule):
 
 
 class TradingDayOfMonthRule(six.with_metaclass(ABCMeta, StatelessRule)):
+
+    @preprocess(n=lossless_float_to_int('TradingDayOfMonthRule'))
     def __init__(self, n, invert):
         if not 0 <= n < MAX_MONTH_RANGE:
             raise _out_of_range_error(MAX_MONTH_RANGE)