From 349e7db5ef5cd7fb20e4aeec047e9d55d683909e Mon Sep 17 00:00:00 2001
From: "Phillip J. Wolfram" <phillipwolfram@gmail.com>
Date: Wed, 11 Jan 2017 09:33:36 -0700
Subject: [PATCH] Fixes too many files open error: h5netcdf backend

---
 xarray/backends/h5netcdf_.py | 44 +++++++++++++++++++++++++-----------
 1 file changed, 31 insertions(+), 13 deletions(-)

diff --git a/xarray/backends/h5netcdf_.py b/xarray/backends/h5netcdf_.py
index 76582cfd72e..0679b928859 100644
--- a/xarray/backends/h5netcdf_.py
+++ b/xarray/backends/h5netcdf_.py
@@ -2,6 +2,7 @@
 from __future__ import division
 from __future__ import print_function
 import functools
+import contextlib
 
 from .. import Variable
 from ..core import indexing
@@ -36,6 +37,11 @@ def _read_attributes(h5netcdf_var):
 _extract_h5nc_encoding = functools.partial(_extract_nc4_encoding,
                                            lsd_okay=False, backend='h5netcdf')
 
+def _close_ds(ds):
+    # netCDF4 only allows closing the root group
+    while ds.parent is not None:
+        ds = ds.parent
+    ds.close()
 
 def _open_h5netcdf_group(filename, mode, group):
     import h5netcdf.legacyapi
@@ -54,12 +60,20 @@ def __init__(self, filename, mode='r', format=None, group=None,
         opener = functools.partial(_open_h5netcdf_group, filename, mode=mode,
                                    group=group)
         self.ds = opener()
+        self._isopen = True
         self.format = format
         self._opener = opener
         self._filename = filename
         self._mode = mode
         super(H5NetCDFStore, self).__init__(writer)
 
+    @contextlib.contextmanager
+    def ensure_open(self):
+        if not self._isopen:
+            self.ds = self._opener()
+            self._isopen = True
+        yield
+
     def open_store_variable(self, name, var):
         dimensions = var.dimensions
         data = indexing.LazilyIndexedArray(BaseNetCDF4Array(name, self))
@@ -77,20 +91,25 @@ def open_store_variable(self, name, var):
         return Variable(dimensions, data, attrs, encoding)
 
     def get_variables(self):
-        return FrozenOrderedDict((k, self.open_store_variable(k, v))
-                                 for k, v in iteritems(self.ds.variables))
+        with self.ensure_open():
+            return FrozenOrderedDict((k, self.open_store_variable(k, v))
+                                     for k, v in iteritems(self.ds.variables))
 
     def get_attrs(self):
-        return Frozen(_read_attributes(self.ds))
+        with self.ensure_open():
+            return Frozen(_read_attributes(self.ds))
 
     def get_dimensions(self):
-        return self.ds.dimensions
+        with self.ensure_open():
+            return self.ds.dimensions
 
     def set_dimension(self, name, length):
-        self.ds.createDimension(name, size=length)
+        with self.ensure_open():
+            self.ds.createDimension(name, size=length)
 
     def set_attribute(self, key, value):
-        self.ds.setncattr(key, value)
+        with self.ensure_open():
+            self.ds.setncattr(key, value)
 
     def prepare_variable(self, name, variable, check_encoding=False):
         import h5py
@@ -123,12 +142,11 @@ def prepare_variable(self, name, variable, check_encoding=False):
         return nc4_var, variable.data
 
     def sync(self):
-        super(H5NetCDFStore, self).sync()
-        self.ds.sync()
+        with self.ensure_open():
+            super(H5NetCDFStore, self).sync()
+            self.ds.sync()
 
     def close(self):
-        ds = self.ds
-        # netCDF4 only allows closing the root group
-        while ds.parent is not None:
-            ds = ds.parent
-        ds.close()
+        if self._isopen:
+            self._isopen = False
+            _close_ds(self.ds)