move bottleneck version warning to Rolling.__init__

xarray/core/ops.py

@@ -18,10 +18,6 @@
 
 try:
     import bottleneck as bn
-    if StrictVersion(bn.__version__) < StrictVersion('1.0'):
-        warnings.warn('xarray requires bottleneck version of 1.0 or greater.'
-                      'Falling back to numpy')
-        raise ImportError('Fall back to numpy')
     has_bottleneck = True
 except ImportError:
     # use numpy methods instead
@@ -509,6 +505,9 @@ def inject_bottleneck_rolling_methods(cls):
 
     # bottleneck rolling methods
     if has_bottleneck:
+        if StrictVersion(bn.__version__) < StrictVersion('1.0'):
+            return
+
         for bn_name, method_name in BOTTLENECK_ROLLING_METHODS.items():
             f = getattr(bn, bn_name)
             func = cls._bottleneck_reduce(f)

xarray/core/rolling.py

@@ -2,11 +2,13 @@
 from __future__ import division
 from __future__ import print_function
 import numpy as np
+import warnings
+from distutils.version import StrictVersion
 
 from .pycompat import OrderedDict, zip
 from .common import ImplementsRollingArrayReduce, full_like
 from .combine import concat
-from .ops import inject_bottleneck_rolling_methods
+from .ops import inject_bottleneck_rolling_methods, has_bottleneck, bn
 
 
 class Rolling(object):
@@ -48,6 +50,13 @@ def __init__(self, obj, min_periods=None, center=False, **windows):
         rolling : type of input argument
         """
 
+        if (has_bottleneck and
+                (StrictVersion(bn.__version__) < StrictVersion('1.0'))):
+            warnings.warn('xarray requires bottleneck version of 1.0 or '
+                          'greater for rolling operations. Rolling '
+                          'aggregation methods will use numpy instead'
+                          'of bottleneck.')
+
         if len(windows) != 1:
             raise ValueError('exactly one dim/window should be provided')
 

xarray/test/__init__.py

@@ -70,8 +70,6 @@
 try:
     import bottleneck
     if StrictVersion(bottleneck.__version__) < StrictVersion('1.0'):
-        warnings.warn('xarray requires bottleneck version of 1.0 or greater.'
-                      'Falling back to numpy')
         raise ImportError('Fall back to numpy')
     has_bottleneck = True
 except ImportError: