expenseAllocation: Switch to own MetadataEnum class.

Python's own enum works fine for the simple values that expenseAllocation
uses, but it won't work as well for metadata like taxImplication where
many of the values aren't legal Python identifiers. Introduce our own
MetadataEnum class with the necessary functionality, and switch to that.

conservancy_beancount/plugin/core.py

@@ -36,6 +36,36 @@ class _GenericRange:
         return self.start <= item < self.stop
 
 
+class MetadataEnum:
+    def __init__(self, key, standard_values, aliases_map):
+        self.key = key
+        self._stdvalues = frozenset(standard_values)
+        self._aliases = dict(aliases_map)
+        self._aliases.update((v, v) for v in standard_values)
+        assert self._stdvalues == set(self._aliases.values())
+
+    def __repr__(self):
+        return "{}<{}>".format(type(self).__name__, self.key)
+
+    def __contains__(self, key):
+        return key in self._aliases
+
+    def __getitem__(self, key):
+        return self._aliases[key]
+
+    def __iter__(self):
+        return iter(self._stdvalues)
+
+    def get(self, key, default_key=None):
+        try:
+            return self[key]
+        except KeyError:
+            if default_key is None:
+                return None
+            else:
+                return self[default_key]
+
+
 class PostingChecker:
     ACCOUNTS = ('',)
     TXN_DATE_RANGE = _GenericRange(DEFAULT_START_DATE, DEFAULT_STOP_DATE)
@@ -76,7 +106,7 @@ class PostingChecker:
                 errors.append(error)
         else:
             try:
-                set_value = self.VALUES_ENUM[source_value].value
+                set_value = self.VALUES_ENUM[source_value]
             except KeyError:
                 errors.append(errormod.InvalidMetadataError(
                     txn, post, self.METADATA_KEY, source_value,

conservancy_beancount/plugin/meta_expense_allocation.py

@@ -14,27 +14,23 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-import enum
-
 from . import core
 
-class ExpenseAllocations(enum.Enum):
-    administration = 'administration'
-    fundraising = 'fundraising'
-    program = 'program'
-
-    admin = administration
-
-
 class MetaExpenseAllocation(core.PostingChecker):
     ACCOUNTS = ('Expenses:',)
     METADATA_KEY = 'expenseAllocation'
-    VALUES_ENUM = ExpenseAllocations
+    VALUES_ENUM = core.MetadataEnum(METADATA_KEY, {
+        'administration',
+        'fundraising',
+        'program',
+    }, {
+        'admin': 'administration',
+    })
     DEFAULT_VALUES = {
-        'Expenses:Services:Accounting': VALUES_ENUM.administration,
-        'Expenses:Services:Administration': VALUES_ENUM.administration,
-        'Expenses:Services:Fundraising': VALUES_ENUM.fundraising,
+        'Expenses:Services:Accounting': VALUES_ENUM['administration'],
+        'Expenses:Services:Administration': VALUES_ENUM['administration'],
+        'Expenses:Services:Fundraising': VALUES_ENUM['fundraising'],
     }
 
     def _default_value(self, txn, post):
-        return self.DEFAULT_VALUES.get(post.account, self.VALUES_ENUM.program).value
+        return self.DEFAULT_VALUES.get(post.account, 'program')