lru metadata manager factory

docs/src/whatsnew/latest.rst

@@ -71,6 +71,19 @@ This document explains the changes made to Iris for this release
    unexpected artifacts in some edge cases, as shown at :issue:`4086`. (:pull:`4150`)
 
 
+🚀 Performance Enhancements
+===========================
+
+#. `@bjlittle`_ added support for automated ``import`` linting with `isort`_, which
+   also includes significant speed-ups for Iris imports. (:pull:`4174`)
+
+#. `@bjlittle`_ Optimised the creation of dynamic metadata manager classes within the
+   :func:`~iris.common.metadata.metadata_manager_factory`, resulting in a significant
+   speed-up in the creation of Iris :class:`~iris.coords.AncillaryVariable`,
+   :class:`~iris.coords.AuxCoord`, :class:`~iris.coords.CellMeasure`, and
+   :class:`~iris.cube.Cube` instances. (:pull:`4227`)
+
+
 💣 Incompatible Changes
 =======================
 
@@ -183,9 +196,6 @@ This document explains the changes made to Iris for this release
 #. `@bjlittle`_ consolidated the ``.flake8`` configuration into ``setup.cfg``.
    (:pull:`4200`)
 
-#. `@bjlittle`_ added support for automated ``import`` linting with `isort`_.
-   (:pull:`4174`)
-
 #. `@bjlittle`_ renamed ``iris/master`` branch to ``iris/main`` and migrated
    references of ``master`` to ``main`` within codebase. (:pull:`4202`)
 

docs/src/whatsnew/latest.rst.template

@@ -58,6 +58,12 @@ This document explains the changes made to Iris for this release
 #. N/A
 
 
+🚀 Performance Enhancements
+===========================
+
+#. N/A
+
+
 🔥 Deprecations
 ===============
 

lib/iris/common/metadata.py

@@ -13,7 +13,7 @@
 from collections import namedtuple
 from collections.abc import Iterable, Mapping
 from copy import deepcopy
-from functools import wraps
+from functools import lru_cache, wraps
 import re
 
 import numpy as np
@@ -1338,39 +1338,19 @@ def equal(self, other, lenient=None):
         return super().equal(other, lenient=lenient)
 
 
-def metadata_manager_factory(cls, **kwargs):
-    """
-    A class instance factory function responsible for manufacturing
-    metadata instances dynamically at runtime.
-
-    The factory instances returned by the factory are capable of managing
-    their metadata state, which can be proxied by the owning container.
-
-    Args:
-
-    * cls:
-        A subclass of :class:`~iris.common.metadata.BaseMetadata`, defining
-        the metadata to be managed.
-
-    Kwargs:
-
-    * kwargs:
-        Initial values for the manufactured metadata instance. Unspecified
-        fields will default to a value of 'None'.
-
-    """
-
+@lru_cache(maxsize=None)
+def _factory_cache(cls):
     def __init__(self, cls, **kwargs):
-        # Restrict to only dealing with appropriate metadata classes.
-        if not issubclass(cls, BaseMetadata):
-            emsg = "Require a subclass of {!r}, got {!r}."
-            raise TypeError(emsg.format(BaseMetadata.__name__, cls))
-
         #: The metadata class to be manufactured by this factory.
         self.cls = cls
 
+        # Proxy for self.cls._fields for later internal use, as this
+        # saves on indirect property lookup via self.cls
+        self._fields = cls._fields
+
         # Initialise the metadata class fields in the instance.
-        for field in self.fields:
+        # Use cls directly here since it's available.
+        for field in cls._fields:
             setattr(self, field, None)
 
         # Populate with provided kwargs, which have already been verified
@@ -1389,7 +1369,7 @@ def __eq__(self, other):
 
     def __getstate__(self):
         """Return the instance state to be pickled."""
-        return {field: getattr(self, field) for field in self.fields}
+        return {field: getattr(self, field) for field in self._fields}
 
     def __ne__(self, other):
         match = self.__eq__(other)
@@ -1412,7 +1392,7 @@ def __repr__(self):
         args = ", ".join(
             [
                 "{}={!r}".format(field, getattr(self, field))
-                for field in self.fields
+                for field in self._fields
             ]
         )
         return "{}({})".format(self.__class__.__name__, args)
@@ -1426,27 +1406,14 @@ def __setstate__(self, state):
     def fields(self):
         """Return the name of the metadata members."""
         # Proxy for built-in namedtuple._fields property.
-        return self.cls._fields
+        return self._fields
 
     @property
     def values(self):
-        fields = {field: getattr(self, field) for field in self.fields}
+        fields = {field: getattr(self, field) for field in self._fields}
         return self.cls(**fields)
 
-    # Restrict factory to appropriate metadata classes only.
-    if not issubclass(cls, BaseMetadata):
-        emsg = "Require a subclass of {!r}, got {!r}."
-        raise TypeError(emsg.format(BaseMetadata.__name__, cls))
-
-    # Check whether kwargs have valid fields for the specified metadata.
-    if kwargs:
-        extra = [field for field in kwargs.keys() if field not in cls._fields]
-        if extra:
-            bad = ", ".join(map(lambda field: "{!r}".format(field), extra))
-            emsg = "Invalid {!r} field parameters, got {}."
-            raise ValueError(emsg.format(cls.__name__, bad))
-
-    # Define the name, (inheritance) bases and namespace of the dynamic class.
+    # Define the name, (inheritance) bases, and namespace of the dynamic class.
     name = "MetadataManager"
     bases = ()
     namespace = {
@@ -1468,12 +1435,52 @@ def values(self):
     if cls is CubeMetadata:
         namespace["_names"] = cls._names
 
-    # Dynamically create the class.
-    Metadata = type(name, bases, namespace)
-    # Now manufacture an instance of that class.
-    metadata = Metadata(cls, **kwargs)
+    # Dynamically create the metadata manager class.
+    MetadataManager = type(name, bases, namespace)
+
+    return MetadataManager
+
+
+def metadata_manager_factory(cls, **kwargs):
+    """
+    A class instance factory function responsible for manufacturing
+    metadata instances dynamically at runtime.
+
+    The factory instances returned by the factory are capable of managing
+    their metadata state, which can be proxied by the owning container.
+
+    Args:
+
+    * cls:
+        A subclass of :class:`~iris.common.metadata.BaseMetadata`, defining
+        the metadata to be managed.
+
+    Kwargs:
+
+    * kwargs:
+        Initial values for the manufactured metadata instance. Unspecified
+        fields will default to a value of 'None'.
+
+    Returns:
+        A manager instance for the provided metadata ``cls``.
+
+    """
+    # Check whether kwargs have valid fields for the specified metadata.
+    if kwargs:
+        extra = [field for field in kwargs.keys() if field not in cls._fields]
+        if extra:
+            bad = ", ".join(map(lambda field: "{!r}".format(field), extra))
+            emsg = "Invalid {!r} field parameters, got {}."
+            raise ValueError(emsg.format(cls.__name__, bad))
+
+    # Dynamically create the metadata manager class at runtime or get a cached
+    # version of it.
+    MetadataManager = _factory_cache(cls)
+
+    # Now manufacture an instance of the metadata manager class.
+    manager = MetadataManager(cls, **kwargs)
 
-    return metadata
+    return manager
 
 
 #: Convenience collection of lenient metadata combine services.

lib/iris/tests/unit/common/metadata/test_metadata_manager_factory.py

@@ -36,14 +36,6 @@
 
 
 class Test_factory(tests.IrisTest):
-    def test__subclass_invalid(self):
-        class Other:
-            pass
-
-        emsg = "Require a subclass of 'BaseMetadata'"
-        with self.assertRaisesRegex(TypeError, emsg):
-            _ = metadata_manager_factory(Other)
-
     def test__kwargs_invalid(self):
         emsg = "Invalid 'BaseMetadata' field parameters, got 'wibble'."
         with self.assertRaisesRegex(ValueError, emsg):
@@ -167,8 +159,8 @@ def setUp(self):
             self.units,
             self.attributes,
         )
-        self.kwargs = dict(zip(BaseMetadata._fields, values))
-        self.metadata = metadata_manager_factory(BaseMetadata, **self.kwargs)
+        kwargs = dict(zip(BaseMetadata._fields, values))
+        self.metadata = metadata_manager_factory(BaseMetadata, **kwargs)
 
     def test_pickle(self):
         for protocol in range(pickle.HIGHEST_PROTOCOL + 1):