Add cube co-realisation.

lib/iris/__init__.py

@@ -112,6 +112,7 @@ def callback(cube, field, filename):
 from iris._deprecation import IrisDeprecation, warn_deprecated
 import iris.fileformats
 import iris.io
+from iris._lazy_data import co_realise_cubes
 
 
 try:
@@ -127,7 +128,7 @@ def callback(cube, field, filename):
 __all__ = ['load', 'load_cube', 'load_cubes', 'load_raw',
            'save', 'Constraint', 'AttributeConstraint', 'sample_data_path',
            'site_configuration', 'Future', 'FUTURE',
-           'IrisDeprecation']
+           'IrisDeprecation', 'co_realise_cubes']
 
 
 Constraint = iris._constraints.Constraint

lib/iris/_lazy_data.py

@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2017, Met Office
+# (C) British Crown Copyright 2017 - 2018, Met Office
 #
 # This file is part of Iris.
 #
@@ -158,3 +158,18 @@ def multidim_lazy_stack(stack):
         result = da.stack([multidim_lazy_stack(subarray)
                            for subarray in stack])
     return result
+
+
+def co_realise_cubes(cubes):
+    """
+    Fetch real data for multiple cubes at one time.
+
+    This fetches lazy content, equivalent to accessing each cube.data.
+    However, lazy calculations and data fetches can be shared between the
+    calculations, improving performance.
+
+    """
+    results = da.compute(list(cube.core_data() for cube in cubes))
+    for cube, result in zip(cubes, results):
+        cube.data = result
+    return cubes