From 72606f740a72d056b07e90e7486942ce6797bbfc Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Tue, 9 Oct 2018 10:34:21 +0200
Subject: [PATCH 01/27] Integration of ECMWF cfgrib driver to read GRIB files
 into xarray.

---
 xarray/backends/__init__.py |   2 +
 xarray/backends/api.py      |   3 +
 xarray/backends/cfgrib_.py  | 125 ++++++++++++++++++++++++++++++++++++
 3 files changed, 130 insertions(+)
 create mode 100644 xarray/backends/cfgrib_.py

diff --git a/xarray/backends/__init__.py b/xarray/backends/__init__.py
index a2f0d79a6d1..9b9e04d9346 100644
--- a/xarray/backends/__init__.py
+++ b/xarray/backends/__init__.py
@@ -5,6 +5,7 @@
 """
 from .common import AbstractDataStore
 from .file_manager import FileManager, CachingFileManager, DummyFileManager
+from .cfgrib_ import CfGribDataStore
 from .memory import InMemoryDataStore
 from .netCDF4_ import NetCDF4DataStore
 from .pydap_ import PydapDataStore
@@ -18,6 +19,7 @@
     'AbstractDataStore',
     'FileManager',
     'CachingFileManager',
+    'CfGribDataStore',
     'DummyFileManager',
     'InMemoryDataStore',
     'NetCDF4DataStore',
diff --git a/xarray/backends/api.py b/xarray/backends/api.py
index 65112527045..f52c32a6d61 100644
--- a/xarray/backends/api.py
+++ b/xarray/backends/api.py
@@ -296,6 +296,9 @@ def maybe_decode_store(store, lock=False):
         elif engine == 'pseudonetcdf':
             store = backends.PseudoNetCDFDataStore.open(
                 filename_or_obj, lock=lock, **backend_kwargs)
+        elif engine == 'cfgrib':
+            store = backends.CfGribDataStore.from_path(
+                filename_or_obj, lock=lock, **backend_kwargs)
         else:
             raise ValueError('unrecognized engine for open_dataset: %r'
                              % engine)
diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
new file mode 100644
index 00000000000..4299de63974
--- /dev/null
+++ b/xarray/backends/cfgrib_.py
@@ -0,0 +1,125 @@
+#
+# Copyright 2017-2018 European Centre for Medium-Range Weather Forecasts (ECMWF).
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# Authors:
+#   Alessandro Amici - B-Open - https://bopen.eu
+#
+
+from __future__ import absolute_import, division, print_function
+
+import numpy as np
+
+from . import common
+from .. import core
+
+
+class WrapGrib(common.BackendArray):
+    def __init__(self, backend_array):
+        self.backend_array = backend_array
+
+    def __getattr__(self, item):
+        return getattr(self.backend_array, item)
+
+    def __getitem__(self, item):
+        key, np_inds = core.indexing.decompose_indexer(
+            item, self.shape, core.indexing.IndexingSupport.OUTER_1VECTOR)
+
+        array = self.backend_array[key.tuple]
+
+        if len(np_inds.tuple) > 0:
+            array = core.indexing.NumpyIndexingAdapter(array)[np_inds]
+
+        return array
+
+
+FLAVOURS = {
+    'eccodes': {
+        'dataset': {
+            'encode_time': False,
+            'encode_vertical': False,
+            'encode_geography': False,
+        },
+    },
+    'ecmwf': {
+        'variable_map': {},
+    },
+    'cds': {
+        'variable_map': {
+            'number': 'realization',
+            'time': 'forecast_reference_time',
+            'valid_time': 'time',
+            'step': 'leadtime',
+            'air_pressure': 'plev',
+            'latitude': 'lat',
+            'longitude': 'lon',
+        },
+    },
+}
+
+
+class CfGribDataStore(common.AbstractDataStore):
+    """
+    Implements the ``xr.AbstractDataStore`` read-only API for a GRIB file.
+    """
+    def __init__(self, ds, variable_map={}, lock=None):
+        self.ds = ds
+        self.variable_map = variable_map.copy()
+        self.lock = lock
+
+    @classmethod
+    def from_path(cls, path, lock=None, flavour_name='ecmwf', errors='ignore', **kwargs):
+        import cfgrib
+        flavour = FLAVOURS[flavour_name].copy()
+        config = flavour.pop('dataset', {}).copy()
+        config.update(kwargs)
+        ds = cfgrib.open_file(path, errors=errors, **config)
+        return cls(ds=ds, lock=lock, **flavour)
+
+    def open_store_variable(self, name, var):
+        if isinstance(var.data, np.ndarray):
+            data = var.data
+        else:
+            data = core.indexing.LazilyOuterIndexedArray(WrapGrib(var.data))
+
+        dimensions = tuple(self.variable_map.get(dim, dim) for dim in var.dimensions)
+        attrs = var.attributes
+
+        # the coordinates attributes need a special treatment
+        if 'coordinates' in attrs:
+            coordinates = [self.variable_map.get(d, d) for d in attrs['coordinates'].split()]
+            attrs['coordinates'] = ' '.join(coordinates)
+
+        encoding = self.ds.encoding.copy()
+        encoding['original_shape'] = var.data.shape
+
+        return core.variable.Variable(dimensions, data, attrs, encoding)
+
+    def get_variables(self):
+        variables = []
+        for k, v in self.ds.variables.items():
+            variables.append((self.variable_map.get(k, k), self.open_store_variable(k, v)))
+        return core.utils.FrozenOrderedDict(variables)
+
+    def get_attrs(self):
+        return core.utils.FrozenOrderedDict(self.ds.attributes)
+
+    def get_dimensions(self):
+        return core.utils.FrozenOrderedDict((self.variable_map.get(d, d), s)
+                                            for d, s in self.ds.dimensions.items())
+
+    def get_encoding(self):
+        encoding = {}
+        encoding['unlimited_dims'] = {k for k, v in self.ds.dimensions.items() if v is None}
+        return encoding

From 71fcbe757b12d93fea95b89e40b4ff59cc992734 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Tue, 9 Oct 2018 21:49:27 +0200
Subject: [PATCH 02/27] Remove all coordinate renaming from the cfgrib backend.

---
 xarray/backends/cfgrib_.py | 36 +++++++-----------------------------
 1 file changed, 7 insertions(+), 29 deletions(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index 4299de63974..580c18372fe 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -52,20 +52,7 @@ def __getitem__(self, item):
             'encode_geography': False,
         },
     },
-    'ecmwf': {
-        'variable_map': {},
-    },
-    'cds': {
-        'variable_map': {
-            'number': 'realization',
-            'time': 'forecast_reference_time',
-            'valid_time': 'time',
-            'step': 'leadtime',
-            'air_pressure': 'plev',
-            'latitude': 'lat',
-            'longitude': 'lon',
-        },
-    },
+    'ecmwf': {},
 }
 
 
@@ -73,13 +60,12 @@ class CfGribDataStore(common.AbstractDataStore):
     """
     Implements the ``xr.AbstractDataStore`` read-only API for a GRIB file.
     """
-    def __init__(self, ds, variable_map={}, lock=None):
+    def __init__(self, ds, lock=False):
         self.ds = ds
-        self.variable_map = variable_map.copy()
         self.lock = lock
 
     @classmethod
-    def from_path(cls, path, lock=None, flavour_name='ecmwf', errors='ignore', **kwargs):
+    def from_path(cls, path, lock=False, flavour_name='ecmwf', errors='ignore', **kwargs):
         import cfgrib
         flavour = FLAVOURS[flavour_name].copy()
         config = flavour.pop('dataset', {}).copy()
@@ -93,31 +79,23 @@ def open_store_variable(self, name, var):
         else:
             data = core.indexing.LazilyOuterIndexedArray(WrapGrib(var.data))
 
-        dimensions = tuple(self.variable_map.get(dim, dim) for dim in var.dimensions)
+        dimensions = var.dimensions
         attrs = var.attributes
 
-        # the coordinates attributes need a special treatment
-        if 'coordinates' in attrs:
-            coordinates = [self.variable_map.get(d, d) for d in attrs['coordinates'].split()]
-            attrs['coordinates'] = ' '.join(coordinates)
-
         encoding = self.ds.encoding.copy()
         encoding['original_shape'] = var.data.shape
 
         return core.variable.Variable(dimensions, data, attrs, encoding)
 
     def get_variables(self):
-        variables = []
-        for k, v in self.ds.variables.items():
-            variables.append((self.variable_map.get(k, k), self.open_store_variable(k, v)))
-        return core.utils.FrozenOrderedDict(variables)
+        return core.utils.FrozenOrderedDict((k, self.open_store_variable(k, v))
+                                            for k, v in self.ds.variables.items())
 
     def get_attrs(self):
         return core.utils.FrozenOrderedDict(self.ds.attributes)
 
     def get_dimensions(self):
-        return core.utils.FrozenOrderedDict((self.variable_map.get(d, d), s)
-                                            for d, s in self.ds.dimensions.items())
+        return core.utils.FrozenOrderedDict(self.ds.dimensions.items())
 
     def get_encoding(self):
         encoding = {}

From 6faa7b9cbc6028dfd23bd52187f9e13a71f7ab7a Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Tue, 9 Oct 2018 22:05:56 +0200
Subject: [PATCH 03/27] Move flavour selection to `cfgrib.Dataset.from_path`.

---
 xarray/backends/cfgrib_.py | 20 ++------------------
 1 file changed, 2 insertions(+), 18 deletions(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index 580c18372fe..5d39b0448a9 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -44,18 +44,6 @@ def __getitem__(self, item):
         return array
 
 
-FLAVOURS = {
-    'eccodes': {
-        'dataset': {
-            'encode_time': False,
-            'encode_vertical': False,
-            'encode_geography': False,
-        },
-    },
-    'ecmwf': {},
-}
-
-
 class CfGribDataStore(common.AbstractDataStore):
     """
     Implements the ``xr.AbstractDataStore`` read-only API for a GRIB file.
@@ -65,13 +53,9 @@ def __init__(self, ds, lock=False):
         self.lock = lock
 
     @classmethod
-    def from_path(cls, path, lock=False, flavour_name='ecmwf', errors='ignore', **kwargs):
+    def from_path(cls, path, lock=False, **backend_kwargs):
         import cfgrib
-        flavour = FLAVOURS[flavour_name].copy()
-        config = flavour.pop('dataset', {}).copy()
-        config.update(kwargs)
-        ds = cfgrib.open_file(path, errors=errors, **config)
-        return cls(ds=ds, lock=lock, **flavour)
+        return cls(ds=cfgrib.open_file(path, **backend_kwargs), lock=lock)
 
     def open_store_variable(self, name, var):
         if isinstance(var.data, np.ndarray):

From 1469a0ebb227ddda94937e55505d2eda28302b03 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Tue, 9 Oct 2018 22:22:51 +0200
Subject: [PATCH 04/27] Sync xarray backend import style with xarray.

---
 xarray/backends/cfgrib_.py | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index 5d39b0448a9..d746d8a1bad 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -21,11 +21,13 @@
 
 import numpy as np
 
-from . import common
-from .. import core
+from .. import Variable
+from ..core import indexing
+from ..core.utils import Frozen, FrozenOrderedDict
+from .common import AbstractDataStore, BackendArray
 
 
-class WrapGrib(common.BackendArray):
+class CfGribArrayWrapper(BackendArray):
     def __init__(self, backend_array):
         self.backend_array = backend_array
 
@@ -33,18 +35,18 @@ def __getattr__(self, item):
         return getattr(self.backend_array, item)
 
     def __getitem__(self, item):
-        key, np_inds = core.indexing.decompose_indexer(
-            item, self.shape, core.indexing.IndexingSupport.OUTER_1VECTOR)
+        key, np_inds = indexing.decompose_indexer(
+            item, self.shape, indexing.IndexingSupport.OUTER_1VECTOR)
 
         array = self.backend_array[key.tuple]
 
         if len(np_inds.tuple) > 0:
-            array = core.indexing.NumpyIndexingAdapter(array)[np_inds]
+            array = indexing.NumpyIndexingAdapter(array)[np_inds]
 
         return array
 
 
-class CfGribDataStore(common.AbstractDataStore):
+class CfGribDataStore(AbstractDataStore):
     """
     Implements the ``xr.AbstractDataStore`` read-only API for a GRIB file.
     """
@@ -61,7 +63,7 @@ def open_store_variable(self, name, var):
         if isinstance(var.data, np.ndarray):
             data = var.data
         else:
-            data = core.indexing.LazilyOuterIndexedArray(WrapGrib(var.data))
+            data = indexing.LazilyOuterIndexedArray(CfGribArrayWrapper(var.data))
 
         dimensions = var.dimensions
         attrs = var.attributes
@@ -69,17 +71,17 @@ def open_store_variable(self, name, var):
         encoding = self.ds.encoding.copy()
         encoding['original_shape'] = var.data.shape
 
-        return core.variable.Variable(dimensions, data, attrs, encoding)
+        return Variable(dimensions, data, attrs, encoding)
 
     def get_variables(self):
-        return core.utils.FrozenOrderedDict((k, self.open_store_variable(k, v))
-                                            for k, v in self.ds.variables.items())
+        return FrozenOrderedDict((k, self.open_store_variable(k, v))
+                                 for k, v in self.ds.variables.items())
 
     def get_attrs(self):
-        return core.utils.FrozenOrderedDict(self.ds.attributes)
+        return Frozen(self.ds.attributes)
 
     def get_dimensions(self):
-        return core.utils.FrozenOrderedDict(self.ds.dimensions.items())
+        return Frozen(self.ds.dimensions)
 
     def get_encoding(self):
         encoding = {}

From 12811e87b9b44647d2542f0648d2543d437ba95f Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Tue, 9 Oct 2018 23:28:49 +0200
Subject: [PATCH 05/27] Make use of the new xarray.backends.FileCachingManager.

---
 xarray/backends/api.py     |  2 +-
 xarray/backends/cfgrib_.py | 22 ++++++++++++----------
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/xarray/backends/api.py b/xarray/backends/api.py
index f52c32a6d61..8816de39a4f 100644
--- a/xarray/backends/api.py
+++ b/xarray/backends/api.py
@@ -297,7 +297,7 @@ def maybe_decode_store(store, lock=False):
             store = backends.PseudoNetCDFDataStore.open(
                 filename_or_obj, lock=lock, **backend_kwargs)
         elif engine == 'cfgrib':
-            store = backends.CfGribDataStore.from_path(
+            store = backends.CfGribDataStore(
                 filename_or_obj, lock=lock, **backend_kwargs)
         else:
             raise ValueError('unrecognized engine for open_dataset: %r'
diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index d746d8a1bad..68c9f801292 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -25,6 +25,7 @@
 from ..core import indexing
 from ..core.utils import Frozen, FrozenOrderedDict
 from .common import AbstractDataStore, BackendArray
+from .file_manager import CachingFileManager
 
 
 class CfGribArrayWrapper(BackendArray):
@@ -50,14 +51,15 @@ class CfGribDataStore(AbstractDataStore):
     """
     Implements the ``xr.AbstractDataStore`` read-only API for a GRIB file.
     """
-    def __init__(self, ds, lock=False):
-        self.ds = ds
+    def __init__(self, filename, lock=False, **backend_kwargs):
+        import cfgrib
         self.lock = lock
+        self._manager = CachingFileManager(
+            cfgrib.open_file, filename, lock=lock, mode='r', **backend_kwargs)
 
-    @classmethod
-    def from_path(cls, path, lock=False, **backend_kwargs):
-        import cfgrib
-        return cls(ds=cfgrib.open_file(path, **backend_kwargs), lock=lock)
+    @property
+    def ds(self):
+        return self._manager.acquire()
 
     def open_store_variable(self, name, var):
         if isinstance(var.data, np.ndarray):
@@ -65,13 +67,10 @@ def open_store_variable(self, name, var):
         else:
             data = indexing.LazilyOuterIndexedArray(CfGribArrayWrapper(var.data))
 
-        dimensions = var.dimensions
-        attrs = var.attributes
-
         encoding = self.ds.encoding.copy()
         encoding['original_shape'] = var.data.shape
 
-        return Variable(dimensions, data, attrs, encoding)
+        return Variable(var.dimensions, data, var.attributes, encoding)
 
     def get_variables(self):
         return FrozenOrderedDict((k, self.open_store_variable(k, v))
@@ -87,3 +86,6 @@ def get_encoding(self):
         encoding = {}
         encoding['unlimited_dims'] = {k for k, v in self.ds.dimensions.items() if v is None}
         return encoding
+
+    def close(self):
+        self._manager.close()

From a4409b657b99d5f9ad4df4df3956adc2a49599fe Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Wed, 10 Oct 2018 00:37:35 +0200
Subject: [PATCH 06/27] Add just-in-case locking for ecCodes.

---
 xarray/backends/cfgrib_.py | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index 68c9f801292..d7e49952a2f 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -26,6 +26,11 @@
 from ..core.utils import Frozen, FrozenOrderedDict
 from .common import AbstractDataStore, BackendArray
 from .file_manager import CachingFileManager
+from .locks import ensure_lock, SerializableLock
+
+# FIXME: Add a dedicated lock just in case, even if ecCodes is supposed to be thread-safe in most
+# circumstances. See: https://confluence.ecmwf.int/display/ECC/Frequently+Asked+Questions
+ECCODES_LOCK = SerializableLock()
 
 
 class CfGribArrayWrapper(BackendArray):
@@ -51,11 +56,14 @@ class CfGribDataStore(AbstractDataStore):
     """
     Implements the ``xr.AbstractDataStore`` read-only API for a GRIB file.
     """
-    def __init__(self, filename, lock=False, **backend_kwargs):
+    def __init__(self, filename, lock=None, **backend_kwargs):
         import cfgrib
-        self.lock = lock
+        if lock is None:
+            lock = ECCODES_LOCK
+        self.lock = ensure_lock(lock)
+        backend_kwargs['filter_by_keys'] = tuple(backend_kwargs.get('filter_by_keys', {}).items())
         self._manager = CachingFileManager(
-            cfgrib.open_file, filename, lock=lock, mode='r', **backend_kwargs)
+            cfgrib.open_file, filename, lock=lock, mode='r', kwargs=backend_kwargs)
 
     @property
     def ds(self):

From 80b8788636aab9f6e7dc8aa9c54c4e7c1308b806 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <alexamici@gmail.com>
Date: Wed, 10 Oct 2018 08:43:11 +0200
Subject: [PATCH 07/27] Explicitly assign attributes to CfGribArrayWrapper

---
 xarray/backends/cfgrib_.py | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index d7e49952a2f..b7c335362c7 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -34,17 +34,16 @@
 
 
 class CfGribArrayWrapper(BackendArray):
-    def __init__(self, backend_array):
-        self.backend_array = backend_array
-
-    def __getattr__(self, item):
-        return getattr(self.backend_array, item)
+    def __init__(self, array):
+        self.shape = array.shape
+        self.dtype = array.dtype
+        self.backend_array = array
 
     def __getitem__(self, item):
         key, np_inds = indexing.decompose_indexer(
             item, self.shape, indexing.IndexingSupport.OUTER_1VECTOR)
 
-        array = self.backend_array[key.tuple]
+        array = self.array[key.tuple]
 
         if len(np_inds.tuple) > 0:
             array = indexing.NumpyIndexingAdapter(array)[np_inds]

From 9dfd6602a350516f00f7eb675864b8d865cfa41d Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Wed, 10 Oct 2018 08:56:23 +0200
Subject: [PATCH 08/27] Add missing locking in CfGribArrayWrapper and use
 explicit_indexing_adapter.

---
 xarray/backends/cfgrib_.py | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index b7c335362c7..878e9f43d86 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -34,21 +34,19 @@
 
 
 class CfGribArrayWrapper(BackendArray):
-    def __init__(self, array):
+    def __init__(self, datastore, array):
+        self.datastore = datastore
         self.shape = array.shape
         self.dtype = array.dtype
-        self.backend_array = array
+        self.array = array
 
-    def __getitem__(self, item):
-        key, np_inds = indexing.decompose_indexer(
-            item, self.shape, indexing.IndexingSupport.OUTER_1VECTOR)
+    def __getitem__(self, key):
+        return indexing.explicit_indexing_adapter(
+            key, self.shape, indexing.IndexingSupport.BASIC, self._getitem)
 
-        array = self.array[key.tuple]
-
-        if len(np_inds.tuple) > 0:
-            array = indexing.NumpyIndexingAdapter(array)[np_inds]
-
-        return array
+    def _getitem(self, key):
+        with self.datastore.lock:
+            return self.array[key]
 
 
 class CfGribDataStore(AbstractDataStore):
@@ -72,7 +70,7 @@ def open_store_variable(self, name, var):
         if isinstance(var.data, np.ndarray):
             data = var.data
         else:
-            data = indexing.LazilyOuterIndexedArray(CfGribArrayWrapper(var.data))
+            data = indexing.LazilyOuterIndexedArray(CfGribArrayWrapper(self, var.data))
 
         encoding = self.ds.encoding.copy()
         encoding['original_shape'] = var.data.shape

From edc4e85e8bdb81b2531a11b40ddab4b382576cbc Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Wed, 10 Oct 2018 21:45:45 +0200
Subject: [PATCH 09/27] Add a comment about the ugly work-around needed for
 filter_by_keys.

---
 xarray/backends/cfgrib_.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index 878e9f43d86..5eca0f7759d 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -58,7 +58,11 @@ def __init__(self, filename, lock=None, **backend_kwargs):
         if lock is None:
             lock = ECCODES_LOCK
         self.lock = ensure_lock(lock)
-        backend_kwargs['filter_by_keys'] = tuple(backend_kwargs.get('filter_by_keys', {}).items())
+
+        # NOTE: filter_by_keys is a dict, but CachingFileManager only accepts hashable types
+        if 'filter_by_keys' in backend_kwargs:
+            backend_kwargs['filter_by_keys'] = tuple(backend_kwargs['filter_by_keys'].items())
+
         self._manager = CachingFileManager(
             cfgrib.open_file, filename, lock=lock, mode='r', kwargs=backend_kwargs)
 

From 9b5335a4499c638e5360bdf58d1295a56c1f9083 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Wed, 10 Oct 2018 22:18:15 +0200
Subject: [PATCH 10/27] Declare correct indexing support.

---
 xarray/backends/cfgrib_.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index 5eca0f7759d..28042e8f1a0 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -42,7 +42,7 @@ def __init__(self, datastore, array):
 
     def __getitem__(self, key):
         return indexing.explicit_indexing_adapter(
-            key, self.shape, indexing.IndexingSupport.BASIC, self._getitem)
+            key, self.shape, indexing.IndexingSupport.OUTER, self._getitem)
 
     def _getitem(self, key):
         with self.datastore.lock:

From 485a40963771a2dc88b6b1aa1277c49a7d86653f Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Sun, 14 Oct 2018 15:16:26 +0200
Subject: [PATCH 11/27] Add TestCfGrib test class.

---
 xarray/tests/__init__.py       |   1 +
 xarray/tests/data/example.grib | Bin 0 -> 5232 bytes
 xarray/tests/test_backends.py  |  19 ++++++++++++++++++-
 3 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 xarray/tests/data/example.grib

diff --git a/xarray/tests/__init__.py b/xarray/tests/__init__.py
index 5f724dd6713..56ecfa30c4d 100644
--- a/xarray/tests/__init__.py
+++ b/xarray/tests/__init__.py
@@ -77,6 +77,7 @@ def LooseVersion(vstring):
 has_zarr, requires_zarr = _importorskip('zarr', minversion='2.2')
 has_np113, requires_np113 = _importorskip('numpy', minversion='1.13.0')
 has_iris, requires_iris = _importorskip('iris')
+has_cfgrib, requires_cfgrib = _importorskip('cfgrib')
 
 # some special cases
 has_scipy_or_netCDF4 = has_scipy or has_netCDF4
diff --git a/xarray/tests/data/example.grib b/xarray/tests/data/example.grib
new file mode 100644
index 0000000000000000000000000000000000000000..596a54d98a022568e41ebe83eedb94d6561a09a6
GIT binary patch
literal 5232
zcmds)F=*6K9LB%2*DFP(hah%v2vSiux84}6cR5do;&g+>41(0j&DM5!4#FuNI*4@W
zkins2Q7Cj1p-}ExXme)=7f%Oq5Uk+PL5csDt1rpLkQeN|YYpEe?_M5Be)s?0_j2Z~
z>sMVDeQ0m*>2OAa3uK@Te$+JH%}<v4dFv$KW!>;bT^ag#1NfPN$ugtwxblP=xw9V_
z@A%Vsfe+RCGjRDB@A7y1@c6ZUa82r@Cm5g|-K$vG2BYH$@62ZDsc?DFnt;%=9A+5q
zGtBPsAz~Y&%}gNUEWIN$e}J9pAX_vb^i#)f3r!2(n4sbf2{Nyiy(25nN69922z_~j
z2E(e2hLM&`ksEK`F#hI7v-k?^L`ThrrXl29LcN8p1=RDY$<(+pj?6qCCDSSp+N@xG
z88sUlD{09TxiOBc@Ht8rM0i()GYw}O%{+#6UlQ|7ksJMN^lm7!v3M<-jduW{rxSRX
z!_*#Tj3BT~f@o^o7)MqbjV8zo9YVi=9Rp1R-|e(yirg4SR-TKJ-EKkXtA&PzH49Gq
zn(?2a`>F5GvydCj;@jvv8v=xOR#1O{Er!~D+L|eHV;q@zF-oT8A+(vtdKI+_HkQ+p
zDRN^RS>aQZEQqjM0+r3#N3(_D5nsK_MtVA#_r~!#fSvAGse@!oz#>5PTJQ$Z`(;})
zWZlU|S+dy#G8<^a5ud=Kh6Guc+;~`Ighg;Ky~>>fge1tiv{HAH`SXm<`2S+YrxI#b
z1?D|0a-+bah76e+H~s_JbAUvADajPMF^=qBLd~dDgk^hW8wG@9YR1iR_$xJCG$tEE
zE45@c(mXo`*%&61%SNghRqm)~W0>qwf*Xm6L^WFi^ni|z8~u3}Ci|bVF*O;@Fj}UM
TK{kfTq_dIcnFvN|a5w%2m#N8p

literal 0
HcmV?d00001

diff --git a/xarray/tests/test_backends.py b/xarray/tests/test_backends.py
index 75aaba718c8..a8d360065e6 100644
--- a/xarray/tests/test_backends.py
+++ b/xarray/tests/test_backends.py
@@ -33,7 +33,7 @@
     has_dask, has_netCDF4, has_scipy, network, raises_regex, requires_cftime,
     requires_dask, requires_h5netcdf, requires_netCDF4, requires_pathlib,
     requires_pseudonetcdf, requires_pydap, requires_pynio, requires_rasterio,
-    requires_scipy, requires_scipy_or_netCDF4, requires_zarr)
+    requires_scipy, requires_scipy_or_netCDF4, requires_zarr, requires_cfgrib)
 from .test_dataset import create_test_data
 
 try:
@@ -2463,6 +2463,23 @@ def test_weakrefs(self):
             assert_identical(actual, expected)
 
 
+@requires_cfgrib
+class TestCfGrib(object):
+
+    def test_read(self):
+        with open_example_dataset('example.grib', engine='cfgrib') as ds:
+            assert ds.dims == {'number': 2, 'time': 3, 'air_pressure': 2, 'latitude': 3, 'longitude': 4}
+            assert list(ds.data_vars) == ['z', 't']
+            assert ds['z'].min() == 12660.
+
+    def test_open_filter_by_keys(self):
+        kwargs = {'filter_by_keys': {'shortName': 't'}}
+        with open_example_dataset('example.grib', engine='cfgrib', backend_kwargs=kwargs) as ds:
+            assert ds.dims == {'number': 2, 'time': 3, 'air_pressure': 2, 'latitude': 3, 'longitude': 4}
+            assert list(ds.data_vars) == ['t']
+            assert ds['t'].min() == 231.
+
+
 @requires_pseudonetcdf
 @pytest.mark.filterwarnings('ignore:IOAPI_ISPH is assumed to be 6370000')
 class TestPseudoNetCDFFormat(object):

From 81f18c2272c3039c14992d4e1795564041bb1cc8 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Sun, 14 Oct 2018 15:17:41 +0200
Subject: [PATCH 12/27] cfgrib doesn't store a file reference so no need for
 CachingFileManager.

---
 xarray/backends/cfgrib_.py | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index 28042e8f1a0..43ca08102fd 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -25,7 +25,6 @@
 from ..core import indexing
 from ..core.utils import Frozen, FrozenOrderedDict
 from .common import AbstractDataStore, BackendArray
-from .file_manager import CachingFileManager
 from .locks import ensure_lock, SerializableLock
 
 # FIXME: Add a dedicated lock just in case, even if ecCodes is supposed to be thread-safe in most
@@ -63,12 +62,7 @@ def __init__(self, filename, lock=None, **backend_kwargs):
         if 'filter_by_keys' in backend_kwargs:
             backend_kwargs['filter_by_keys'] = tuple(backend_kwargs['filter_by_keys'].items())
 
-        self._manager = CachingFileManager(
-            cfgrib.open_file, filename, lock=lock, mode='r', kwargs=backend_kwargs)
-
-    @property
-    def ds(self):
-        return self._manager.acquire()
+        self.ds = cfgrib.open_file(filename, mode='r', **backend_kwargs)
 
     def open_store_variable(self, name, var):
         if isinstance(var.data, np.ndarray):
@@ -95,6 +89,3 @@ def get_encoding(self):
         encoding = {}
         encoding['unlimited_dims'] = {k for k, v in self.ds.dimensions.items() if v is None}
         return encoding
-
-    def close(self):
-        self._manager.close()

From 5dedb3fc65fce12e36e395d532875d2f69328f2f Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Sun, 14 Oct 2018 16:40:34 +0200
Subject: [PATCH 13/27] Add cfgrib testing to Travis-CI.

---
 ci/requirements-py36.yml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/ci/requirements-py36.yml b/ci/requirements-py36.yml
index fd63fe26130..fc272984237 100644
--- a/ci/requirements-py36.yml
+++ b/ci/requirements-py36.yml
@@ -21,8 +21,10 @@ dependencies:
   - bottleneck
   - zarr
   - pseudonetcdf>=3.0.1
+  - eccodes
   - pip:
     - coveralls
     - pytest-cov
     - pydap
     - lxml
+    - cfgrib

From 831ae4f27bff2d3d2adcdfe08721abb58464df14 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Sun, 14 Oct 2018 16:50:10 +0200
Subject: [PATCH 14/27] Naming.

---
 xarray/tests/test_backends.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xarray/tests/test_backends.py b/xarray/tests/test_backends.py
index a8d360065e6..3fe13c2ee67 100644
--- a/xarray/tests/test_backends.py
+++ b/xarray/tests/test_backends.py
@@ -2472,7 +2472,7 @@ def test_read(self):
             assert list(ds.data_vars) == ['z', 't']
             assert ds['z'].min() == 12660.
 
-    def test_open_filter_by_keys(self):
+    def test_read_filter_by_keys(self):
         kwargs = {'filter_by_keys': {'shortName': 't'}}
         with open_example_dataset('example.grib', engine='cfgrib', backend_kwargs=kwargs) as ds:
             assert ds.dims == {'number': 2, 'time': 3, 'air_pressure': 2, 'latitude': 3, 'longitude': 4}

From 6372e6eec6f962af8e8d64f5afe632c0296d87c3 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Sun, 14 Oct 2018 17:06:55 +0200
Subject: [PATCH 15/27] Fix line lengths and get to 100% coverage.

---
 xarray/backends/cfgrib_.py    | 22 ++++++++++++++--------
 xarray/tests/test_backends.py | 11 ++++++++---
 2 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index 43ca08102fd..23b7761a450 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -1,5 +1,5 @@
 #
-# Copyright 2017-2018 European Centre for Medium-Range Weather Forecasts (ECMWF).
+# Copyright 2017-2018 European Centre for Medium-Range Weather Forecasts.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -27,8 +27,9 @@
 from .common import AbstractDataStore, BackendArray
 from .locks import ensure_lock, SerializableLock
 
-# FIXME: Add a dedicated lock just in case, even if ecCodes is supposed to be thread-safe in most
-# circumstances. See: https://confluence.ecmwf.int/display/ECC/Frequently+Asked+Questions
+# FIXME: Add a dedicated lock, even if ecCodes is supposed to be thread-safe
+# in most circumstances. See:
+#   https://confluence.ecmwf.int/display/ECC/Frequently+Asked+Questions
 ECCODES_LOCK = SerializableLock()
 
 
@@ -58,9 +59,11 @@ def __init__(self, filename, lock=None, **backend_kwargs):
             lock = ECCODES_LOCK
         self.lock = ensure_lock(lock)
 
-        # NOTE: filter_by_keys is a dict, but CachingFileManager only accepts hashable types
+        # NOTE: filter_by_keys is a dict, but CachingFileManager only accepts
+        #   hashable types.
         if 'filter_by_keys' in backend_kwargs:
-            backend_kwargs['filter_by_keys'] = tuple(backend_kwargs['filter_by_keys'].items())
+            filter_by_keys_items = backend_kwargs['filter_by_keys'].items()
+            backend_kwargs['filter_by_keys'] = tuple(filter_by_keys_items)
 
         self.ds = cfgrib.open_file(filename, mode='r', **backend_kwargs)
 
@@ -68,7 +71,8 @@ def open_store_variable(self, name, var):
         if isinstance(var.data, np.ndarray):
             data = var.data
         else:
-            data = indexing.LazilyOuterIndexedArray(CfGribArrayWrapper(self, var.data))
+            wrapped_array = CfGribArrayWrapper(self, var.data)
+            data = indexing.LazilyOuterIndexedArray(wrapped_array)
 
         encoding = self.ds.encoding.copy()
         encoding['original_shape'] = var.data.shape
@@ -86,6 +90,8 @@ def get_dimensions(self):
         return Frozen(self.ds.dimensions)
 
     def get_encoding(self):
-        encoding = {}
-        encoding['unlimited_dims'] = {k for k, v in self.ds.dimensions.items() if v is None}
+        dims = self.get_dimensions()
+        encoding = {
+            'unlimited_dims': {k for k, v in dims.items() if v is None},
+        }
         return encoding
diff --git a/xarray/tests/test_backends.py b/xarray/tests/test_backends.py
index 3fe13c2ee67..a274b41c424 100644
--- a/xarray/tests/test_backends.py
+++ b/xarray/tests/test_backends.py
@@ -2467,15 +2467,20 @@ def test_weakrefs(self):
 class TestCfGrib(object):
 
     def test_read(self):
+        expected = {'number': 2, 'time': 3, 'air_pressure': 2, 'latitude': 3,
+                    'longitude': 4}
         with open_example_dataset('example.grib', engine='cfgrib') as ds:
-            assert ds.dims == {'number': 2, 'time': 3, 'air_pressure': 2, 'latitude': 3, 'longitude': 4}
+            assert ds.dims == expected
             assert list(ds.data_vars) == ['z', 't']
             assert ds['z'].min() == 12660.
 
     def test_read_filter_by_keys(self):
         kwargs = {'filter_by_keys': {'shortName': 't'}}
-        with open_example_dataset('example.grib', engine='cfgrib', backend_kwargs=kwargs) as ds:
-            assert ds.dims == {'number': 2, 'time': 3, 'air_pressure': 2, 'latitude': 3, 'longitude': 4}
+        expected = {'number': 2, 'time': 3, 'air_pressure': 2, 'latitude': 3,
+                    'longitude': 4}
+        with open_example_dataset('example.grib', engine='cfgrib',
+                                  backend_kwargs=kwargs) as ds:
+            assert ds.dims == expected
             assert list(ds.data_vars) == ['t']
             assert ds['t'].min() == 231.
 

From 8e9b2e37bb07e42c808717fea1d82a2a267c66d8 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Sun, 14 Oct 2018 20:58:52 +0200
Subject: [PATCH 16/27] Add reference to *cfgrib* engine in inline docs.

---
 xarray/backends/api.py | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/xarray/backends/api.py b/xarray/backends/api.py
index 8816de39a4f..3fb7338e171 100644
--- a/xarray/backends/api.py
+++ b/xarray/backends/api.py
@@ -162,7 +162,8 @@ def open_dataset(filename_or_obj, group=None, decode_cf=True,
     decode_coords : bool, optional
         If True, decode the 'coordinates' attribute to identify coordinates in
         the resulting dataset.
-    engine : {'netcdf4', 'scipy', 'pydap', 'h5netcdf', 'pynio', 'pseudonetcdf'}, optional
+    engine : {'netcdf4', 'scipy', 'pydap', 'h5netcdf', 'pynio', 'cfgrib',
+        'pseudonetcdf'}, optional
         Engine to use when reading files. If not provided, the default engine
         is chosen based on available dependencies, with a preference for
         'netcdf4'.
@@ -359,7 +360,8 @@ def open_dataarray(filename_or_obj, group=None, decode_cf=True,
     decode_coords : bool, optional
         If True, decode the 'coordinates' attribute to identify coordinates in
         the resulting dataset.
-    engine : {'netcdf4', 'scipy', 'pydap', 'h5netcdf', 'pynio'}, optional
+    engine : {'netcdf4', 'scipy', 'pydap', 'h5netcdf', 'pynio', 'cfgrib'},
+        optional
         Engine to use when reading files. If not provided, the default engine
         is chosen based on available dependencies, with a preference for
         'netcdf4'.
@@ -489,7 +491,8 @@ def open_mfdataset(paths, chunks=None, concat_dim=_CONCAT_DIM_DEFAULT,
           of all non-null values.
     preprocess : callable, optional
         If provided, call this function on each dataset prior to concatenation.
-    engine : {'netcdf4', 'scipy', 'pydap', 'h5netcdf', 'pynio'}, optional
+    engine : {'netcdf4', 'scipy', 'pydap', 'h5netcdf', 'pynio', 'cfgrib'},
+        optional
         Engine to use when reading files. If not provided, the default engine
         is chosen based on available dependencies, with a preference for
         'netcdf4'.

From 07b946909249e4df667ee12c137b06d7bf3367a2 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Sun, 14 Oct 2018 21:21:57 +0200
Subject: [PATCH 17/27] First cut of the documentation.

---
 doc/installing.rst |  4 +++-
 doc/io.rst         | 17 +++++++++++++++++
 doc/whats-new.rst  |  6 +++++-
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/doc/installing.rst b/doc/installing.rst
index eb74eb7162b..64751eea637 100644
--- a/doc/installing.rst
+++ b/doc/installing.rst
@@ -34,7 +34,9 @@ For netCDF and IO
 - `rasterio <https://github.com/mapbox/rasterio>`__: for reading GeoTiffs and
   other gridded raster datasets.
 - `iris <https://github.com/scitools/iris>`__: for conversion to and from iris'
-  Cube objects.
+  Cube objects
+- `cfgrib <https://github.com/ecmwf/cfgrib>`__: for reading GRIB files via the
+  *ECMWF ecCodes* library.
 
 For accelerating xarray
 ~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/doc/io.rst b/doc/io.rst
index 093ee773e15..cfe552d1d54 100644
--- a/doc/io.rst
+++ b/doc/io.rst
@@ -635,6 +635,23 @@ For example:
     Not all native zarr compression and filtering options have been tested with
     xarray.
 
+.. _io.cfgrib:
+
+GRIB format via cfgrib
+----------------------
+
+xarray supports reading GRIB files via ECMWF cfgrib_ python driver and ecCodes_
+C-library, if they are installed. To open GRIB file supply ``engine='cfgrib'``
+to :py:func:`~xarray.open_dataset`:
+
+We recommend installing ecCodes via conda::
+
+    conda install -c conda-forge eccodes
+    pip install cfgrib
+
+.. _cfgrib: https://github.com/ecmwf/cfgrib
+.. _ecCodes: https://confluence.ecmwf.int/display/ECC/ecCodes+Home
+
 .. _io.pynio:
 
 Formats supported by PyNIO
diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index c8ae5ac43c8..31771020c84 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -72,7 +72,11 @@ Enhancements
   :py:meth:`~xarray.DataArray.interp`, and
   :py:meth:`~xarray.Dataset.interp`.
   By `Spencer Clark <https://github.com/spencerkclark>`_
-  
+- Added a new backend for the GRIB file format based on ECMWF *cfgrib*
+  python driver and *ecCodes* C-library. (:issue:`2475`)
+  By `Alessandro Amici <https://github.com/alexamici>`_,
+  sponsored by `ECMWF <https://github.com/ecmwf>`_.
+
 Bug fixes
 ~~~~~~~~~
 

From 340720a4e68dc4638e2d99cf7fd8d3191927e4f1 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Mon, 15 Oct 2018 00:16:44 +0200
Subject: [PATCH 18/27] Tentative test cfgrib under dask.distributed.

---
 xarray/tests/test_distributed.py | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/xarray/tests/test_distributed.py b/xarray/tests/test_distributed.py
index 7c77a62d3c9..764d2c7d4b5 100644
--- a/xarray/tests/test_distributed.py
+++ b/xarray/tests/test_distributed.py
@@ -20,12 +20,12 @@
 import xarray as xr
 from xarray.backends.locks import HDF5_LOCK, CombinedLock
 from xarray.tests.test_backends import (ON_WINDOWS, create_tmp_file,
-                                        create_tmp_geotiff)
+                                        create_tmp_geotiff, open_example_dataset)
 from xarray.tests.test_dataset import create_test_data
 
 from . import (
     assert_allclose, has_h5netcdf, has_netCDF4, requires_rasterio, has_scipy,
-    requires_zarr, raises_regex)
+    requires_zarr, requires_cfgrib, raises_regex)
 
 # this is to stop isort throwing errors. May have been easier to just use
 # `isort:skip` in retrospect
@@ -142,6 +142,18 @@ def test_dask_distributed_rasterio_integration_test(loop):
                 assert_allclose(actual, expected)
 
 
+@requires_cfgrib
+def test_dask_distributed_cfgrib_integration_test(loop):
+    with cluster() as (s, [a, b]):
+        with Client(s['address'], loop=loop) as c:
+            ds = open_example_dataset('example.grib', engine='cfgrib', chunks={'time': 1})
+            da_grib = ds['t']
+            assert isinstance(da_grib.data, da.Array)
+            actual = da_grib.compute()
+            assert actual.dims == ('number', 'time', 'air_pressure', 'latitude', 'longitude')
+            assert actual.coords['time'].size == 3
+
+
 @pytest.mark.skipif(distributed.__version__ <= '1.19.3',
                     reason='Need recent distributed version to clean up get')
 @gen_cluster(client=True, timeout=None)

From 4d84f708fb5f1f8a1712fb5bc9a1ab7fb4a23588 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Mon, 15 Oct 2018 00:25:05 +0200
Subject: [PATCH 19/27] Better integration test.

---
 xarray/tests/test_distributed.py | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/xarray/tests/test_distributed.py b/xarray/tests/test_distributed.py
index 764d2c7d4b5..9af1ca02408 100644
--- a/xarray/tests/test_distributed.py
+++ b/xarray/tests/test_distributed.py
@@ -146,12 +146,14 @@ def test_dask_distributed_rasterio_integration_test(loop):
 def test_dask_distributed_cfgrib_integration_test(loop):
     with cluster() as (s, [a, b]):
         with Client(s['address'], loop=loop) as c:
-            ds = open_example_dataset('example.grib', engine='cfgrib', chunks={'time': 1})
-            da_grib = ds['t']
-            assert isinstance(da_grib.data, da.Array)
-            actual = da_grib.compute()
-            assert actual.dims == ('number', 'time', 'air_pressure', 'latitude', 'longitude')
-            assert actual.coords['time'].size == 3
+            with open_example_dataset('example.grib',
+                                      engine='cfgrib',
+                                      chunks={'time': 1}) as ds:
+                with open_example_dataset('example.grib',
+                                          engine='cfgrib') as expected:
+                    assert isinstance(ds['t'].data, da.Array)
+                    actual = ds.compute()
+                    assert_allclose(actual, expected)
 
 
 @pytest.mark.skipif(distributed.__version__ <= '1.19.3',

From 0b027db7ef3bd90ec7a3f22c74772fed1f21e241 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Mon, 15 Oct 2018 11:27:52 +0200
Subject: [PATCH 20/27] Remove explicit copyright and license boilerplate to
 harmonise with other files.

---
 xarray/backends/cfgrib_.py | 19 -------------------
 1 file changed, 19 deletions(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index 23b7761a450..fbe39bcdb1f 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -1,22 +1,3 @@
-#
-# Copyright 2017-2018 European Centre for Medium-Range Weather Forecasts.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#   http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-#
-# Authors:
-#   Alessandro Amici - B-Open - https://bopen.eu
-#
-
 from __future__ import absolute_import, division, print_function
 
 import numpy as np

From a4ead545f1a19ad62802a16284817c04d739dd79 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Mon, 15 Oct 2018 11:34:37 +0200
Subject: [PATCH 21/27] Add a usage example.

---
 doc/io.rst | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/doc/io.rst b/doc/io.rst
index cfe552d1d54..2363146ce0b 100644
--- a/doc/io.rst
+++ b/doc/io.rst
@@ -641,9 +641,13 @@ GRIB format via cfgrib
 ----------------------
 
 xarray supports reading GRIB files via ECMWF cfgrib_ python driver and ecCodes_
-C-library, if they are installed. To open GRIB file supply ``engine='cfgrib'``
+C-library, if they are installed. To open a GRIB file supply ``engine='cfgrib'``
 to :py:func:`~xarray.open_dataset`:
 
+.. ipython:: python
+
+    ds_grib = xr.open_dataset('example.grib', engine='cfgrib')
+
 We recommend installing ecCodes via conda::
 
     conda install -c conda-forge eccodes

From ec80d86e43d418c26349dbfb785d11f030027a70 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Mon, 15 Oct 2018 15:59:38 +0200
Subject: [PATCH 22/27] Fix code style.

---
 xarray/tests/test_distributed.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xarray/tests/test_distributed.py b/xarray/tests/test_distributed.py
index 9af1ca02408..1837a0fe4ef 100644
--- a/xarray/tests/test_distributed.py
+++ b/xarray/tests/test_distributed.py
@@ -20,7 +20,8 @@
 import xarray as xr
 from xarray.backends.locks import HDF5_LOCK, CombinedLock
 from xarray.tests.test_backends import (ON_WINDOWS, create_tmp_file,
-                                        create_tmp_geotiff, open_example_dataset)
+                                        create_tmp_geotiff,
+                                        open_example_dataset)
 from xarray.tests.test_dataset import create_test_data
 
 from . import (

From f30b7d0bbc71756be8d768c76caf7330b3e62afa Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Tue, 16 Oct 2018 12:43:35 +0200
Subject: [PATCH 23/27] Fix doc style.

---
 xarray/backends/cfgrib_.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xarray/backends/cfgrib_.py b/xarray/backends/cfgrib_.py
index fbe39bcdb1f..c0a7c025606 100644
--- a/xarray/backends/cfgrib_.py
+++ b/xarray/backends/cfgrib_.py
@@ -9,8 +9,8 @@
 from .locks import ensure_lock, SerializableLock
 
 # FIXME: Add a dedicated lock, even if ecCodes is supposed to be thread-safe
-# in most circumstances. See:
-#   https://confluence.ecmwf.int/display/ECC/Frequently+Asked+Questions
+#   in most circumstances. See:
+#       https://confluence.ecmwf.int/display/ECC/Frequently+Asked+Questions
 ECCODES_LOCK = SerializableLock()
 
 

From 223d25c16d4e3394051426ad7532888f2a9561b6 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Wed, 17 Oct 2018 08:57:30 +0200
Subject: [PATCH 24/27] Fix docs testing. The example.grib file is not
 accessible.

---
 doc/io.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/io.rst b/doc/io.rst
index 2363146ce0b..9e7a94e2646 100644
--- a/doc/io.rst
+++ b/doc/io.rst
@@ -645,6 +645,7 @@ C-library, if they are installed. To open a GRIB file supply ``engine='cfgrib'``
 to :py:func:`~xarray.open_dataset`:
 
 .. ipython:: python
+    :verbatim:
 
     ds_grib = xr.open_dataset('example.grib', engine='cfgrib')
 

From bbf01e30088010fe334fbc3ee815719e4122b03f Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Wed, 17 Oct 2018 09:00:21 +0200
Subject: [PATCH 25/27] Fix merge in docs.

---
 doc/whats-new.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index 2b5696ec3a7..03404e7e6b6 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -71,7 +71,7 @@ Enhancements
   :py:meth:`~xarray.Dataset.differentiate`,
   :py:meth:`~xarray.DataArray.interp`, and
   :py:meth:`~xarray.Dataset.interp`.
-  By `Spencer Clark <https://github.com/spencerkclark>`_
+  By `Spencer Clark <https://github.com/spencerkclark>`_.
 - Added a new backend for the GRIB file format based on ECMWF *cfgrib*
   python driver and *ecCodes* C-library. (:issue:`2475`)
   By `Alessandro Amici <https://github.com/alexamici>`_,

From da2b9ddca940b627168781dfc14594c1367010f0 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Wed, 17 Oct 2018 09:00:42 +0200
Subject: [PATCH 26/27] Fix merge in docs.

---
 doc/whats-new.rst | 2 --
 1 file changed, 2 deletions(-)

diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index 03404e7e6b6..61da801badb 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -77,8 +77,6 @@ Enhancements
   By `Alessandro Amici <https://github.com/alexamici>`_,
   sponsored by `ECMWF <https://github.com/ecmwf>`_.
 
-  By `Spencer Clark <https://github.com/spencerkclark>`_.
-  
 Bug fixes
 ~~~~~~~~~
 

From eda96a495844fdff53a0da9a35e56a3f3e575267 Mon Sep 17 00:00:00 2001
From: Alessandro Amici <a.amici@bopen.eu>
Date: Wed, 17 Oct 2018 17:52:04 +0200
Subject: [PATCH 27/27] Fix doc style.

---
 doc/io.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/doc/io.rst b/doc/io.rst
index 9e7a94e2646..e841e665308 100644
--- a/doc/io.rst
+++ b/doc/io.rst
@@ -644,10 +644,10 @@ xarray supports reading GRIB files via ECMWF cfgrib_ python driver and ecCodes_
 C-library, if they are installed. To open a GRIB file supply ``engine='cfgrib'``
 to :py:func:`~xarray.open_dataset`:
 
-.. ipython:: python
+.. ipython::
     :verbatim:
 
-    ds_grib = xr.open_dataset('example.grib', engine='cfgrib')
+    In [1]: ds_grib = xr.open_dataset('example.grib', engine='cfgrib')
 
 We recommend installing ecCodes via conda::