DOC: added some missing docstrings

src/caosdb/common/datatype.py

@@ -60,10 +60,21 @@ def is_list_datatype(datatype):
 
 
 def is_reference(datatype):
-    """ returns whether the value is a reference
+    """Returns whether the value is a reference
 
     FILE and REFERENCE properties are examples, but also datatypes that are
-    RecordTypes
+    RecordTypes.
+
+    Parameters
+    ----------
+    datatype : str
+               The datatype to check.
+
+    Returns
+    -------
+    bool
+        True if the datatype is a not base datatype or a list of a base datatype.
+        Otherwise False is returned.
     """
 
     if datatype in [DOUBLE, BOOLEAN, INTEGER, TEXT, DATETIME]:
@@ -73,6 +84,39 @@ def is_reference(datatype):
     else:
         return True
 
+def get_referenced_recordtype(datatype):
+    """Return the record type of the referenced datatype.
+
+    Raises
+    ------
+    ValueError
+              In cases where datatype is not a reference, the list does not have
+              a referenced record type or the datatype is a FILE.
+
+    Parameters
+    ----------
+    datatype : str
+               The datatype to check.
+
+    Returns
+    -------
+    str
+       String containing the name of the referenced datatype.
+    """
+
+    if not is_reference(datatype):
+        raise ValueError("datatype must be a reference")
+
+    if is_list_datatype(datatype):
+        datatype = get_list_datatype(datatype)
+        if datatype is None:
+            raise ValueError("list does not have a list datatype")
+
+    if datatype == FILE:
+        raise ValueError("FILE references are not considered references with a record type")
+
+    return datatype
+
 
 def get_id_of_datatype(datatype):
     """ returns the id of a Record Type