Fixes too many files open error: pynio backend

xarray/backends/pynio_.py

@@ -3,10 +3,12 @@
 from __future__ import print_function
 
 import functools
+import contextlib
 
 import numpy as np
 
 from .. import Variable
+from .netCDF4_ import VariableWrapper
 from ..core.utils import FrozenOrderedDict, Frozen, NDArrayMixin
 from ..core import indexing
 
@@ -21,16 +23,18 @@ def __init__(self, variable_name, datastore):
 
     @property
     def array(self):
-        return self.datastore.ds.variables[self.variable_name]
+        with self.datastore.ensure_open():
+            return VariableWrapper(self.datastore, self.variable_name)
 
     @property
     def dtype(self):
         return np.dtype(self.array.typecode())
 
     def __getitem__(self, key):
-        if key == () and self.ndim == 0:
-            return self.array.get_value()
-        return self.array[key]
+        with self.datastore.ensure_open():
+            if key == () and self.ndim == 0:
+                return self.array.get_value()
+            return self.array[key]
 
 
 class NioDataStore(AbstractDataStore, DataStorePickleMixin):
@@ -40,22 +44,39 @@ def __init__(self, filename, mode='r'):
         import Nio
         opener = functools.partial(Nio.open_file, filename, mode=mode)
         self.ds = opener()
+        self._isopen = True
         self._opener = opener
         self._mode = mode
 
+    @contextlib.contextmanager
+    def ensure_open(self, autoclose=True):
+        if not self._isopen:
+            try:
+                self.ds = self._opener()
+                self._isopen = True
+                yield
+            finally:
+                if autoclose:
+                    self.close()
+        else:
+            yield
+
     def open_store_variable(self, name, var):
         data = indexing.LazilyIndexedArray(NioArrayWrapper(name, self))
         return Variable(var.dimensions, data, var.attributes)
 
     def get_variables(self):
-        return FrozenOrderedDict((k, self.open_store_variable(k, v))
-                                 for k, v in self.ds.variables.iteritems())
+        with self.ensure_open():
+            return FrozenOrderedDict((k, self.open_store_variable(k, v))
+                                     for k, v in self.ds.variables.iteritems())
 
     def get_attrs(self):
-        return Frozen(self.ds.attributes)
+        with self.ensure_open():
+            return Frozen(self.ds.attributes)
 
     def get_dimensions(self):
-        return Frozen(self.ds.dimensions)
+        with self.ensure_open():
+            return Frozen(self.ds.dimensions)
 
     def get_encoding(self):
         encoding = {}
@@ -64,4 +85,6 @@ def get_encoding(self):
         return encoding
 
     def close(self):
-        self.ds.close()
+        if self._isopen:
+            self.ds.close()
+            self._isopen = False