Add method for loading registry from a Python module (#386)

intake_esm/derived.py

@@ -1,3 +1,5 @@
+import importlib
+import inspect
 import typing
 
 import pydantic
@@ -34,6 +36,43 @@ class DerivedVariableRegistry:
     def __post_init_post_parse__(self):
         self._registry = {}
 
+    @classmethod
+    def load(cls, name: str, package: str = None) -> 'DerivedVariableRegistry':
+        """Load a DerivedVariableRegistry from a Python module/file
+
+        Parameters
+        ----------
+        name : str
+            The name of the module to load the DerivedVariableRegistry from.
+        package : str, optional
+            The package to load the module from. This argument is
+            required when performing a relative import. It specifies the package
+            to use as the anchor point from which to resolve the relative import
+            to an absolute import.
+
+        Returns
+        -------
+        DerivedVariableRegistry
+            A DerivedVariableRegistry loaded from the Python module.
+
+        Notes
+        -----
+        If you have a folder: /home/foo/pythonfiles, and you want to load a registry
+        defined in registry.py, located in that directory, ensure to add your folder to the
+        $PYTHONPATH before calling this function.
+
+        >>> import sys
+        >>> sys.path.insert(0, "/home/foo/pythonfiles")
+        >>> from intake_esm.derived import DerivedVariableRegistry
+        >>> registsry = DerivedVariableRegistry.load("registry")
+        """
+        modname = importlib.import_module(name, package=package)
+        candidates = inspect.getmembers(modname, lambda x: isinstance(x, DerivedVariableRegistry))
+        if candidates:
+            return candidates[0][1]
+        else:
+            raise ValueError(f'No DerivedVariableRegistry found in {name} module')
+
     @tlz.curry
     def register(
         self, func: typing.Callable, *, variable: str, dependent_variables: typing.List[str]

tests/my_registry.py

@@ -0,0 +1,8 @@
+import intake_esm
+
+registry = intake_esm.DerivedVariableRegistry()
+
+
+@registry.register(variable='FOO', dependent_variables=['FLUT'])
+def func(ds):
+    return ds

tests/test_derived.py

@@ -1,8 +1,12 @@
+import sys
+
 import pytest
 import xarray as xr
 
 from intake_esm.derived import DerivedVariable, DerivedVariableError, DerivedVariableRegistry
 
+from .utils import here
+
 
 def test_registry_init():
     """
@@ -14,6 +18,18 @@ def test_registry_init():
     assert len(dvr.keys()) == 0
 
 
+def test_registry_load():
+
+    sys.path.insert(0, f'{here}/')
+    dvr = DerivedVariableRegistry.load('my_registry')
+    assert len(dvr) > 0
+    assert 'FOO' in dvr
+
+    # Test for errors/ invalid inputs, wrong return type
+    with pytest.raises(ValueError):
+        DerivedVariableRegistry.load('utils')
+
+
 def test_registry_register():
     dvr = DerivedVariableRegistry()