STY: Fix flake8 failures.

tests/events/test_events.py

@@ -21,7 +21,6 @@ from nose_parameterized import parameterized
 import pandas as pd
 from six import iteritems
 from six.moves import range, map
-from toolz import concat
 
 import zipline.utils.events
 from zipline.utils.calendars import get_calendar

tests/pipeline/test_blaze.py

@@ -41,7 +41,6 @@ from zipline.testing import (
 from zipline.testing.fixtures import WithAssetFinder
 from zipline.testing.predicates import assert_equal, assert_isidentical
 from zipline.utils.numpy_utils import float64_dtype, int64_dtype
-from zipline.utils.pandas_utils import ignore_pandas_nan_categorical_warning
 
 
 nameof = op.attrgetter('name')

tests/pipeline/test_engine.py

@@ -1141,10 +1141,10 @@ class ParameterizedFactorTestCase(WithTradingEnvironment, ZiplineTestCase):
         alpha = 1 - decay_rate
         span = (2 / alpha) - 1
 
-        # XXX: This is a comically inefficient way to compute a windowed EWMSTD.
-        # Don't use it outside of testing.  We're using rolling-apply of an
-        # ewma (which is itself a rolling-window function) because we only want
-        # to look at ``window_length`` rows at a time.
+        # XXX: This is a comically inefficient way to compute a windowed
+        # EWMSTD.  Don't use it outside of testing.  We're using rolling-apply
+        # of an ewma (which is itself a rolling-window function) because we
+        # only want to look at ``window_length`` rows at a time.
         return rolling_apply(
             self.raw_data,
             window_length,