Defer loading the default DD definitions

imas/backends/db_entry_impl.py

@@ -78,7 +78,7 @@ def get(
         destination: IDSToplevel,
         lazy: bool,
         nbc_map: Optional[NBCPathMap],
-    ) -> None:
+    ) -> IDSToplevel:
         """Implement DBEntry.get/get_slice/get_sample. Load data from the data source.
 
         Args:

imas/db_entry.py

@@ -160,7 +160,7 @@ def __init__(
                 legacy = True
             except TypeError as exc2:
                 raise TypeError(
-                    f"Incorrect arguments to {__class__.__name__}.__init__(): "
+                    "Incorrect arguments to DBEntry.__init__(): "
                     f"{exc1.args[0]}, {exc2.args[0]}"
                 ) from None
 
@@ -561,7 +561,7 @@ def _get(
             raise RuntimeError("Database entry is not open.")
         if lazy and destination:
             raise ValueError("Cannot supply a destination IDS when lazy loading.")
-        if not self._ids_factory.exists(ids_name):
+        if autoconvert and not self._ids_factory.exists(ids_name):
             raise IDSNameError(ids_name, self._ids_factory)
 
         # Note: this will raise an exception when the ids/occurrence is not filled:
@@ -577,7 +577,7 @@ def _get(
                 ids_name,
                 occurrence,
             )
-        elif dd_version != self.dd_version and dd_version not in dd_xml_versions():
+        elif dd_version not in dd_xml_versions() and dd_version != self.dd_version:
             # We don't know the DD version that this IDS was written with
             if ignore_unknown_dd_version:
                 # User chooses to ignore this problem, load as if it was stored with

imas/ids_factory.py

@@ -41,6 +41,17 @@ def __init__(
             version: DD version string, e.g. "3.38.1".
             xml_path: XML file containing data dictionary definition.
         """
+        if version is None and xml_path is None:
+            # Defer loading the DD definitions until we really need them
+            self.__deferred_init = True
+        else:
+            # If a specific version or xml_path is requested, we still load immediately
+            # so any exceptions are raise when creating the IDSfactory
+            self.__do_init(version, xml_path)
+            self.__deferred_init = False
+
+    def __do_init(self, version: str | None, xml_path: str | pathlib.Path | None):
+        """Actual initialization logic"""
         self._xml_path = xml_path
         self._etree = dd_zip.dd_etree(version, xml_path)
         self._ids_elements = {
@@ -71,10 +82,16 @@ def __dir__(self) -> Iterable[str]:
         return sorted(set(object.__dir__(self)).union(self._ids_elements))
 
     def __getattr__(self, name: str) -> Any:
+        # Actually initialize when we deferred it before
+        if self.__deferred_init:
+            self.__do_init(None, None)
+            self.__deferred_init = False
+            return getattr(self, name)
+        # Check if the name matches any IDS and return a 'constructor' for it
         if name in self._ids_elements:
             # Note: returning a partial to mimic AL HLI, e.g. factory.core_profiles()
             return partial(IDSToplevel, self, self._ids_elements[name])
-        raise AttributeError(f"{type(self)!r} object has no attribute {name!r}")
+        raise AttributeError(f"'IDSFactory' has no attribute {name!r}")
 
     def __iter__(self) -> Iterator[str]:
         """Iterate over the IDS names defined by the loaded Data Dictionary"""