ENH: Don't add a metadata instance with only one object

docs/source/utils.rst

@@ -10,6 +10,7 @@ utils.py
    safe_load
    get_current_experiment
    IterableNamespace
+   count_ns_leaves
    extract_objs
    find_object
    find_class

hutch_python/load_conf.py

@@ -19,7 +19,8 @@
 from .namespace import class_namespace, metadata_namespace
 from .qs_load import get_qs_objs
 from .user_load import get_user_objs
-from .utils import get_current_experiment, safe_load, hutch_banner
+from .utils import (get_current_experiment, safe_load, hutch_banner,
+                    count_ns_leaves)
 
 logger = logging.getLogger(__name__)
 
@@ -238,7 +239,11 @@ def load_conf(conf, hutch_dir=None):
         if hutch is not None:
             meta = metadata_namespace(['beamline', 'stand'],
                                       scope='hutch_python.db')
-            cache(**meta.__dict__)
+            # Prune meta, remove branches with only one object
+            for name, space in meta.__dict__.items():
+                if count_ns_leaves(space) > 1:
+                    cache(**{name: space})
+
         default_class_namespace(object, 'all_objects', cache)
 
     # Write db.txt info file to the user's module

hutch_python/tests/test_load_conf.py

@@ -17,6 +17,7 @@ def test_file_load():
     err = '{} was overriden by a namespace'
     for elem in should_have:
         assert not isinstance(objs[elem], SimpleNamespace), err.format(elem)
+    assert 'tst' in objs
 
 
 def test_no_file():

hutch_python/tests/test_utils.py

@@ -34,6 +34,22 @@ def test_iterable_namespace():
     assert len(ns) == 3
 
 
+def test_count_leaves():
+    logger.debug('test_count_leaves')
+
+    ns0 = utils.IterableNamespace(a=utils.IterableNamespace())
+    ns1 = utils.IterableNamespace(a=1, b=utils.IterableNamespace())
+    ns2 = utils.IterableNamespace(a=utils.IterableNamespace(a=1),
+                                  b=utils.IterableNamespace(b=2))
+    ns3 = utils.IterableNamespace(a=1,
+                                  b=utils.IterableNamespace(a=1, b=2))
+
+    assert utils.count_ns_leaves(ns0) == 0
+    assert utils.count_ns_leaves(ns1) == 1
+    assert utils.count_ns_leaves(ns2) == 2
+    assert utils.count_ns_leaves(ns3) == 3
+
+
 def test_extract_objs():
     logger.debug('test_extract_objs')
     # Has no __all__ keyword

hutch_python/utils.py

@@ -94,6 +94,23 @@ def __len__(self):
         return len(self.__dict__)
 
 
+def count_ns_leaves(namespace):
+    """
+    Count the number of objects in a nested `IterableNamespace`.
+
+    Given an `IterableNamespace` that contains other `IterableNamespace`
+    objects that may in themselves contain `IterableNamespace` objects,
+    determine how many non-`IterableNamespace` objects are in the tree.
+    """
+    count = 0
+    for obj in namespace:
+        if isinstance(obj, IterableNamespace):
+            count += count_ns_leaves(obj)
+        else:
+            count += 1
+    return count
+
+
 def extract_objs(scope=None, skip_hidden=True, stack_offset=0):
     """
     Return all objects with the ``scope``.