Add NameConstraint with relaxed name loading

docs/iris/src/userguide/loading_iris_cubes.rst

@@ -166,18 +166,36 @@ As we have seen, loading the following file creates several Cubes::
     cubes = iris.load(filename)
 
 Specifying a name as a constraint argument to :py:func:`iris.load` will mean 
-only cubes with a matching :meth:`name <iris.cube.Cube.name>` 
+only cubes with matching :meth:`name <iris.cube.Cube.names>`
 will be returned::
 
     filename = iris.sample_data_path('uk_hires.pp')
-    cubes = iris.load(filename, 'specific_humidity')
+    cubes = iris.load(filename, 'surface_altitude')
 
-To constrain the load to multiple distinct constraints, a list of constraints 
+Note that, the provided name will match against either the standard name,
+long name, NetCDF variable name or STASH metadata of a cube. Therefore, the
+previous example using the ``surface_altitude`` standard name constraint can
+also be achieved using the STASH value of ``m01s00i033``::
+
+    filename = iris.sample_data_path('uk_hires.pp')
+    cubes = iris.load(filename, 'm01s00i033')
+
+If further specific name constraint control is required i.e., to constrain
+against a combination of standard name, long name, NetCDF variable name and/or
+STASH metadata, consider using the :class:`iris.NameConstraint`. For example,
+to constrain against both a standard name of ``surface_altitude`` **and** a STASH
+of ``m01s00i033``::
+
+    filename = iris.sample_data_path('uk_hires.pp')
+    constraint = iris.NameConstraint(standard_name='surface_altitude', STASH='m01s00i033')
+    cubes = iris.load(filename, constraint)
+
+To constrain the load to multiple distinct constraints, a list of constraints
 can be provided.  This is equivalent to running load once for each constraint 
 but is likely to be more efficient::
 
     filename = iris.sample_data_path('uk_hires.pp')
-    cubes = iris.load(filename, ['air_potential_temperature', 'specific_humidity'])
+    cubes = iris.load(filename, ['air_potential_temperature', 'surface_altitude'])
 
 The :class:`iris.Constraint` class can be used to restrict coordinate values 
 on load. For example, to constrain the load to match 

docs/iris/src/whatsnew/contributions_3.0.0/newfeature_2019-Oct-15_nameconstraint.txt

@@ -0,0 +1 @@
+* The :class:`~iris.NameConstraint` provides richer name constraint matching when loading or extracting against cubes, by supporting a constraint against any combination of ``standard_name``, ``long_name``, NetCDF ``var_name`` and ``STASH`` from the attributes dictionary of a :class:`~iris.cube.Cube`.

docs/iris/src/whatsnew/contributions_3.0.0/newfeature_2019-Oct-15_names_property.txt

@@ -0,0 +1 @@
+* Cubes and coordinates now have a new ``names`` property that contains a tuple of the ``standard_name``, ``long_name``, NetCDF ``var_name``, and ``STASH`` attributes metadata.

docs/iris/src/whatsnew/contributions_3.0.0/newfeature_2019-Oct-15_relaxed_name_loading.txt

@@ -0,0 +1 @@
+* Name constraint matching against cubes during loading or extracting has been relaxed from strictly matching against the :meth:`~iris.cube.Cube.name`, to matching against either the ``standard_name``, ``long_name``, NetCDF ``var_name``, or ``STASH`` attributes metadata of a cube.

lib/iris/__init__.py

@@ -117,6 +117,7 @@ def callback(cube, field, filename):
     "save",
     "Constraint",
     "AttributeConstraint",
+    "NameConstraint",
     "sample_data_path",
     "site_configuration",
     "Future",
@@ -127,6 +128,7 @@ def callback(cube, field, filename):
 
 Constraint = iris._constraints.Constraint
 AttributeConstraint = iris._constraints.AttributeConstraint
+NameConstraint = iris._constraints.NameConstraint
 
 
 class Future(threading.local):

lib/iris/_constraints.py

@@ -35,7 +35,8 @@ def __init__(self, name=None, cube_func=None, coord_values=None, **kwargs):
         Args:
 
         * name:   string or None
-            If a string, it is used as the name to match against Cube.name().
+            If a string, it is used as the name to match against the
+            `~iris.cube.Cube.names` property.
         * cube_func:   callable or None
             If a callable, it must accept a Cube as its first and only argument
             and return either True or False.
@@ -128,7 +129,9 @@ def _coordless_match(self, cube):
         """
         match = True
         if self._name:
-            match = self._name == cube.name()
+            # Require to also check against cube.name() for the fallback
+            # "unknown" default case, when there is no name metadata available.
+            match = self._name in cube.names or self._name == cube.name()
         if match and self._cube_func:
             match = self._cube_func(cube)
         return match
@@ -466,7 +469,7 @@ def __init__(self, **attributes):
 
         """
         self._attributes = attributes
-        Constraint.__init__(self, cube_func=self._cube_func)
+        super().__init__(cube_func=self._cube_func)
 
     def _cube_func(self, cube):
         match = True
@@ -490,3 +493,107 @@ def _cube_func(self, cube):
 
     def __repr__(self):
         return "AttributeConstraint(%r)" % self._attributes
+
+
+class NameConstraint(Constraint):
+    """Provides a simple Cube name based :class:`Constraint`."""
+
+    def __init__(
+        self,
+        standard_name="none",
+        long_name="none",
+        var_name="none",
+        STASH="none",
+    ):
+        """
+        Provides a simple Cube name based :class:`Constraint`, which matches
+        against each of the names provided, which may be either standard name,
+        long name, NetCDF variable name and/or the STASH from the attributes
+        dictionary.
+
+        The name constraint will only succeed if *all* of the provided names
+        match.
+
+        Kwargs:
+        * standard_name:
+            A string or callable representing the standard name to match
+            against.
+        * long_name:
+            A string or callable representing the long name to match against.
+        * var_name:
+            A string or callable representing the NetCDF variable name to match
+            against.
+        * STASH:
+            A string or callable representing the UM STASH code to match
+            against.
+
+        .. note::
+            The default value of each of the keyword arguments is the string
+            "none", rather than the singleton None, as None may be a legitimate
+            value to be matched against e.g., to constrain against all cubes
+            where the standard_name is not set, then use standard_name=None.
+
+        ... note::
+            The None value will not be passed through to a callable. Instead
+            use the "<name>=None" pattern.
+
+        Returns:
+        * Boolean
+
+        Example usage::
+
+            iris.NameConstraint(long_name='air temp', var_name=None)
+
+            iris.NameConstraint(long_name=lambda name: 'temp' in name)
+
+            iris.NameConstraint(standard_name='air_temperature',
+                                STASH=lambda stash: stash.item == 203)
+
+        """
+        self.standard_name = standard_name
+        self.long_name = long_name
+        self.var_name = var_name
+        self.STASH = STASH
+        self._names = ("standard_name", "long_name", "var_name", "STASH")
+        super().__init__(cube_func=self._cube_func)
+
+    def _cube_func(self, cube):
+        def matcher(target, value):
+            if callable(value):
+                result = False
+                if target is not None:
+                    #
+                    # Don't pass None through into the callable. Users should
+                    # use the "name=None" pattern instead. Otherwise, users
+                    # will need to explicitly handle the None case, which is
+                    # unnecessary and pretty darn ugly e.g.,
+                    #
+                    # lambda name: name is not None and name.startswith('ick')
+                    #
+                    result = value(target)
+            else:
+                result = value == target
+            return result
+
+        match = True
+        for name in self._names:
+            expected = getattr(self, name)
+            if expected != "none":
+                if name == "STASH":
+                    actual = cube.attributes.get(name)
+                else:
+                    actual = getattr(cube, name)
+                match = matcher(actual, expected)
+                # Make this is a short-circuit match.
+                if match is False:
+                    break
+
+        return match
+
+    def __repr__(self):
+        names = []
+        for name in self._names:
+            value = getattr(self, name)
+            if value != "none":
+                names.append("{}={!r}".format(name, value))
+        return "{}({})".format(self.__class__.__name__, ", ".join(names))

lib/iris/_cube_coord_common.py

@@ -4,6 +4,8 @@
 # See COPYING and COPYING.LESSER in the root of the repository for full
 # licensing details.
 
+
+from collections import namedtuple
 import re
 
 import cf_units
@@ -15,6 +17,30 @@
 _TOKEN_PARSE = re.compile(r"""^[a-zA-Z0-9][\w\.\+\-@]*$""")
 
 
+class Names(
+    namedtuple("Names", ["standard_name", "long_name", "var_name", "STASH"])
+):
+    """
+    Immutable container for name metadata.
+
+    Args:
+
+    * standard_name:
+        A string representing the CF Conventions and Metadata standard name, or
+        None.
+    * long_name:
+        A string representing the CF Conventions and Metadata long name, or
+        None
+    * var_name:
+        A string representing the associated NetCDF variable name, or None.
+    * STASH:
+        A string representing the `~iris.fileformats.pp.STASH` code, or None.
+
+    """
+
+    __slots__ = ()
+
+
 def get_valid_standard_name(name):
     # Standard names are optionally followed by a standard name
     # modifier, separated by one or more blank spaces
@@ -181,6 +207,22 @@ def _check(item):
 
         return result
 
+    @property
+    def names(self):
+        """
+        A tuple containing all of the metadata names. This includes the
+        standard name, long name, NetCDF variable name, and attributes
+        STASH name.
+
+        """
+        standard_name = self.standard_name
+        long_name = self.long_name
+        var_name = self.var_name
+        stash_name = self.attributes.get("STASH")
+        if stash_name is not None:
+            stash_name = str(stash_name)
+        return Names(standard_name, long_name, var_name, stash_name)
+
     def rename(self, name):
         """
         Changes the human-readable name.