[GH#71] Take into account identifier aliases

docs/source/identifiers.rst

@@ -11,13 +11,16 @@ enumerated list of options for defining, for example:
   a neutron, or a photon.
 - Plasma heating may come from neutral beam injection, electron cyclotron heating,
   ion cyclotron heating, lower hybrid heating, alpha particles.
+- These may have alternative naming conventions supported through aliases 
+  (e.g., "235U" and "U_235" for Uranium 235).
 
-Identifiers are a list of possible valid labels. Each label has three
+Identifiers are a list of possible valid labels. Each label has up to four
 representations:
 
 1. An index (integer)
 2. A name (short string)
 3. A description (long string)
+4. List of aliases (list of short strings)
 
 
 Identifiers in IMAS-Python
@@ -44,6 +47,14 @@ the available identifiers is stored as ``imas.identifiers.identifiers``.
     print(csid.total.index)
     print(csid.total.description)
 
+    # Access identifiers with aliases (when available)
+    mid = imas.identifiers.materials_identifier
+    print(mid["235U"])        # Access by canonical name
+    print(mid["U_235"])       # Access by alias
+
+    # Both return the same object
+    assert mid["235U"] is mid["U_235"]
+
     # Item access is also possible
     print(identifiers["edge_source_identifier"])
 
@@ -64,8 +75,8 @@ Assigning identifiers in IMAS-Python
 
 IMAS-Python implements smart assignment of identifiers. You may assign an identifier
 enum value (for example ``imas.identifiers.core_source_identifier.total``), a
-string (for example ``"total"``) or an integer (for example ``"1"``) to an
-identifier structure (for example ``core_profiles.source[0].identifier``) to set
+string (for example ``"total"`` or its alias), or an integer (for example ``"1"``) 
+to an identifier structure (for example ``core_profiles.source[0].identifier``) to set
 all three child nodes ``name``, ``index`` and ``description`` in one go. See
 below example:
 
@@ -86,6 +97,15 @@ below example:
     # 3. Assign an integer. This looks up the index in the identifier enum:
     core_sources.source[0].identifier = 1
 
+    # Identifiers can still be assigned with the old alias name for backward compatibility:
+    materials = imas.IDSFactory().materials()
+    materials.material.resize(1)
+    mid = imas.identifiers.materials_identifier
+    # Assign using canonical name
+    materials.material[0].identifier = "235U"
+    # Or assign using alias (equivalent to above)
+    materials.material[0].identifier = "U_235"
+
     # Inspect the contents of the structure
     imas.util.inspect(core_sources.source[0].identifier)
 
@@ -101,18 +121,72 @@ below example:
     imas.util.inspect(core_sources.source[1].identifier)
 
 
+Identifier aliases
+------------------
+
+Some identifiers may have multiple aliases defined in the Data Dictionary. Aliases are
+former names kept as an option to ensure better backward compatibility after a change
+and support multiple naming conventions. An identifier can have any number of
+comma-separated aliases.
+
+Aliases can be accessed in the same ways as canonical names, and all aliases for an
+identifier point to the same object.
+
+Aliases that begin with a number (e.g., 235U) cannot be accessed using dot notation 
+(e.g., material_identifier.235U) due to Python's syntax restrictions. Instead, such
+aliases must be accessed using dictionary-style indexing, for example:
+material_identifier["235U"].
+
+.. code-block:: python
+    :caption: Working with identifier aliases
+
+    import imas
+
+    # Get materials identifier which has some aliases defined
+    mid = imas.identifiers.materials_identifier
+
+    # Access by canonical name
+    uranium235_by_name = mid["235U"]
+    print(f"Name: {uranium235_by_name.name}")
+    print(f"Aliases: {uranium235_by_name.aliases}")  # List of all aliases
+    print(f"First alias: {uranium235_by_name.alias}")  # First alias for compatibility
+    print(f"Index: {uranium235_by_name.index}")
+    print(f"Description: {uranium235_by_name.description}")
+
+    # Access by any alias - all return the same object
+    uranium235_by_alias1 = mid["U_235"]
+    uranium235_by_alias2 = mid["Uranium_235"]
+    print(f"Same objects: {uranium235_by_name is uranium235_by_alias1 is uranium235_by_alias2}")
+
+    # You can also use attribute access for aliases (when valid Python identifiers)
+    uranium235_by_attr = mid.U_235
+    print(f"Same object: {uranium235_by_name is uranium235_by_attr}")
+
+    # When assigning to IDS structures, any alias works the same way
+    materials = imas.IDSFactory().materials()
+    materials.material.resize(1)
+
+    # These assignments are all equivalent:
+    materials.material[0].identifier = "235U"          # canonical name
+    materials.material[0].identifier = "U_235"         # first alias
+    materials.material[0].identifier = "Uranium_235"   # another alias
+    materials.material[0].identifier = mid["235U"]     # enum value
+    materials.material[0].identifier = mid.U_235       # enum value via alias
+
+
 Compare identifiers
 -------------------
 
 Identifier structures can be compared against the identifier enum as well. They
 compare equal when:
 
 1.  ``index`` is an exact match
-2.  ``name`` is an exact match, or ``name`` is not filled in the IDS node
+2.  ``name`` is an exact match, or ``name`` matches an alias, or ``name`` is not filled in the IDS node
 
 The ``description`` does not have to match with the Data Dictionary definition,
 but a warning is logged if the description in the IDS node does not match with
-the Data Dictionary description:
+the Data Dictionary description. The comparison also takes aliases into account,
+so an identifier will match both its canonical name and any defined alias:
 
 .. code-block:: python
     :caption: Comparing identifiers
@@ -139,6 +213,15 @@ the Data Dictionary description:
     >>> core_sources.source[0].identifier.name = "totalX"
     >>> core_sources.source[0].identifier == csid.total
     False
+    >>> # Alias comparison example with materials identifier
+    >>> mid = imas.identifiers.materials_identifier
+    >>> materials = imas.IDSFactory().materials()
+    >>> materials.material.resize(1)
+    >>> materials.material[0].identifier.index = 20
+    >>> materials.material[0].identifier.name = "U_235"  # Using alias
+    >>> # Compares equal to the canonical identifier even though name is alias
+    >>> materials.material[0].identifier == mid["235U"]
+    True
 
 
 .. seealso::

imas/ids_identifiers.py

@@ -1,7 +1,6 @@
 # This file is part of IMAS-Python.
 # You should have received the IMAS-Python LICENSE file with this project.
-"""IMAS-Python module to support Data Dictionary identifiers.
-"""
+"""IMAS-Python module to support Data Dictionary identifiers."""
 
 import logging
 from enum import Enum
@@ -16,16 +15,18 @@
 class IDSIdentifier(Enum):
     """Base class for all identifier enums."""
 
-    def __new__(self, value: int, description: str):
-        obj = object.__new__(self)
+    def __new__(cls, value: int, description: str, aliases: list = []):
+        obj = object.__new__(cls)
         obj._value_ = value
         return obj
 
-    def __init__(self, value: int, description: str) -> None:
+    def __init__(self, value: int, description: str, aliases: list = []) -> None:
         self.index = value
         """Unique index for this identifier value."""
         self.description = description
         """Description for this identifier value."""
+        self.aliases = aliases
+        """Alternative names for this identifier value."""
 
     def __eq__(self, other):
         if self is other:
@@ -37,35 +38,49 @@ def __eq__(self, other):
         except (AttributeError, TypeError, ValueError):
             # Attribute doesn't exist, or failed to convert
             return NotImplemented
+
         # Index must match
         if other_index == self.index:
-            # Name may be left empty
-            if other_name == self.name or other_name == "":
+            # Name may be left empty, or match name or alias
+            if (
+                other_name == self.name
+                or other_name == ""
+                or other_name in self.aliases
+            ):
                 # Description doesn't have to match, though we will warn when it doesn't
-                if other_description != self.description and other_description != "":
+                if other_description not in (self.description, ""):
                     logger.warning(
                         "Description of %r does not match identifier description %r",
                         other.description,
                         self.description,
                     )
                 return True
-            else:
-                logger.warning(
-                    "Name %r does not match identifier name %r, but indexes are equal.",
-                    other.name,
-                    self.name,
-                )
+
+            # If we get here with matching indexes but no name/alias match, warn
+            logger.warning(
+                "Name %r does not match identifier name %r, but indexes are equal.",
+                other.name,
+                self.name,
+            )
         return False
 
     @classmethod
     def _from_xml(cls, identifier_name, xml) -> Type["IDSIdentifier"]:
         element = fromstring(xml)
         enum_values = {}
+        aliases = {}
         for int_element in element.iterfind("int"):
             name = int_element.get("name")
             value = int_element.text
             description = int_element.get("description")
-            enum_values[name] = (int(value), description)
+            # alias attribute may contain multiple comma-separated aliases
+            alias_attr = int_element.get("alias", "")
+            aliases = [a.strip() for a in alias_attr.split(",") if a.strip()]
+            # Canonical entry: use the canonical 'name' as key
+            enum_values[name] = (int(value), description, aliases)
+            # Also add alias names as enum *aliases* (they become enum attributes)
+            for alias in aliases:
+                enum_values[alias] = (int(value), description, aliases)
         # Create the enumeration
         enum = cls(
             identifier_name,