python: rework creating of Subclasses

Add some smart magic, so that when we invoke a
NotmuchError(STATUSVALUE), a nicely derived subclass is created, e.g. a
OutOfMemoryError. This way users can easily distinguish between error
types, while still catching NotmuchError.

I have tested this, and hope it works for others too.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

2 files changed, 36 insertions, 22 deletions

diff --git a/bindings/python/notmuch/database.py b/bindings/python/notmuch/database.py
index 644e2e5f..f1c1eb75 100644
--- a/bindings/python/notmuch/database.py
+++ b/bindings/python/notmuch/database.py
@@ -112,7 +112,7 @@ class Database(object):
     def _assert_db_is_initialized(self):
         """Raises a NotmuchError in case self._db is still None"""
         if self._db is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NOT_INITIALIZED)
+            raise NotmuchError(STATUS.NOT_INITIALIZED)
 
     def create(self, path):
         """Creates a new notmuch database
@@ -231,7 +231,7 @@ class Database(object):
         self._assert_db_is_initialized()
         status = nmlib.notmuch_database_begin_atomic(self._db)
         if status != STATUS.SUCCESS:
-            raise NotmuchError.get_subclass_exc(status)
+            raise NotmuchError(status)
         return status
 
     def end_atomic(self):
@@ -253,7 +253,7 @@ class Database(object):
         self._assert_db_is_initialized()
         status = nmlib.notmuch_database_end_atomic(self._db)
         if status != STATUS.SUCCESS:
-            raise NotmuchError.get_subclass_exc(status)
+            raise NotmuchError(status)
         return status
 
     def get_directory(self, path):
@@ -284,7 +284,7 @@ class Database(object):
             # we got an absolute path
             if not path.startswith(self.get_path()):
                 # but its initial components are not equal to the db path
-                raise NotmuchError.get_subclass_exc(STATUS.FILE_ERROR,
+                raise NotmuchError(STATUS.FILE_ERROR,
                                    message="Database().get_directory() called "
                                            "with a wrong absolute path.")
             abs_dirpath = path
@@ -355,7 +355,7 @@ class Database(object):
                                                   byref(msg_p))
 
         if not status in [STATUS.SUCCESS, STATUS.DUPLICATE_MESSAGE_ID]:
-            raise NotmuchError.get_subclass_exc(status)
+            raise NotmuchError(status)
 
         #construct Message() and return
         msg = Message(msg_p, self)
@@ -449,7 +449,7 @@ class Database(object):
         self._assert_db_is_initialized()
         tags_p = Database._get_all_tags(self._db)
         if tags_p == None:
-            raise NotmuchError.get_subclass_exc(STATUS.NULL_POINTER)
+            raise NotmuchError(STATUS.NULL_POINTER)
         return Tags(tags_p, self)
 
     def create_query(self, querystring):
@@ -573,13 +573,13 @@ class Query(object):
                         (too little memory)
         """
         if db.db_p is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NOT_INITIALIZED)
+            raise NotmuchError(STATUS.NOT_INITIALIZED)
         # create reference to parent db to keep it alive
         self._db = db
         # create query, return None if too little mem available
         query_p = Query._create(db.db_p, _str(querystr))
         if query_p is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NULL_POINTER)
+            raise NotmuchError(STATUS.NULL_POINTER)
         self._query = query_p
 
     def set_sort(self, sort):
@@ -593,7 +593,7 @@ class Query(object):
                     been initialized.
         """
         if self._query is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NOT_INITIALIZED)
+            raise NotmuchError(STATUS.NOT_INITIALIZED)
 
         self.sort = sort
         nmlib.notmuch_query_set_sort(self._query, sort)
@@ -619,7 +619,7 @@ class Query(object):
                       * :attr:`STATUS`.NULL_POINTER if search_threads failed
         """
         if self._query is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NOT_INITIALIZED)
+            raise NotmuchError(STATUS.NOT_INITIALIZED)
 
         threads_p = Query._search_threads(self._query)
 
@@ -642,12 +642,12 @@ class Query(object):
                       * :attr:`STATUS`.NULL_POINTER if search_messages failed
         """
         if self._query is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NOT_INITIALIZED)
+            raise NotmuchError(STATUS.NOT_INITIALIZED)
 
         msgs_p = Query._search_messages(self._query)
 
         if msgs_p is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NULL_POINTER)
+            raise NotmuchError(STATUS.NULL_POINTER)
 
         return Messages(msgs_p, self)
 
@@ -667,7 +667,7 @@ class Query(object):
                       * :attr:`STATUS`.NOT_INITIALIZED if query is not inited
         """
         if self._query is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NOT_INITIALIZED)
+            raise NotmuchError(STATUS.NOT_INITIALIZED)
 
         return Query._count_messages(self._query)
 
@@ -710,7 +710,7 @@ class Directory(object):
     def _assert_dir_is_initialized(self):
         """Raises a NotmuchError(:attr:`STATUS`.NOT_INITIALIZED) if dir_p is None"""
         if self._dir_p is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NOT_INITIALIZED)
+            raise NotmuchError(STATUS.NOT_INITIALIZED)
 
     def __init__(self, path, dir_p, parent):
         """
@@ -770,7 +770,7 @@ class Directory(object):
         if status == STATUS.SUCCESS:
             return
         #fail with Exception otherwise
-        raise NotmuchError.get_subclass_exc(status)
+        raise NotmuchError(status)
 
     def get_mtime(self):
         """Gets the mtime value of this directory in the database
@@ -856,7 +856,7 @@ class Filenames(object):
 
     def next(self):
         if self._files_p is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NOT_INITIALIZED)
+            raise NotmuchError(STATUS.NOT_INITIALIZED)
 
         if not nmlib.notmuch_filenames_valid(self._files_p):
             self._files_p = None
@@ -879,7 +879,7 @@ class Filenames(object):
                      for file in files: print file
         """
         if self._files_p is None:
-            raise NotmuchError.get_subclass_exc(STATUS.NOT_INITIALIZED)
+            raise NotmuchError(STATUS.NOT_INITIALIZED)
 
         i = 0
         while nmlib.notmuch_filenames_valid(self._files_p):
diff --git a/bindings/python/notmuch/globals.py b/bindings/python/notmuch/globals.py
index 5fca3d9b..190854a1 100644
--- a/bindings/python/notmuch/globals.py
+++ b/bindings/python/notmuch/globals.py
@@ -96,7 +96,7 @@ class NotmuchError(Exception):
     but SUCCESS has a corresponding subclassed Exception."""
 
     @classmethod
-    def get_subclass_exc(cls, status, message=None):
+    def get_exc_subclass(cls, status):
         """Returns a fine grained Exception() type,detailing the error status"""
         subclasses = {
             STATUS.OUT_OF_MEMORY: OutOfMemoryError,
@@ -112,9 +112,23 @@ class NotmuchError(Exception):
             STATUS.NOT_INITIALIZED: NotInitializedError
         }
         assert 0 < status <= len(subclasses)
-        return subclasses[status](status, message)
-
-    def __init__(self, status, message=None):
+        return subclasses[status]
+
+    def __new__(cls, *args, **kwargs):
+        """Return a correct subclass of NotmuchError if needed
+
+        We return a NotmuchError instance if status is None (or 0) and a
+        subclass that inherits from NotmuchError depending on the
+        'status' parameter otherwise."""
+        # get 'status'. Passed in as arg or kwarg?
+        status = args[0] if len(args) else kwargs.get('status', None)
+        # no 'status' or cls is subclass already, return 'cls' instance
+        if not status or cls != NotmuchError:
+            return super(NotmuchError, cls).__new__(cls)
+        subclass = cls.get_exc_subclass(status) # which class to use?
+        return subclass.__new__(subclass, *args, **kwargs)
+
+    def __init__(self, status=None, message=None):
         self.status = status
         self.message = message
 
@@ -127,7 +141,7 @@ class NotmuchError(Exception):
             return 'Unknown error'
 
 # List of Subclassed exceptions that correspond to STATUS values and are
-# subclasses of NotmuchError:
+# subclasses of NotmuchError.
 class OutOfMemoryError(NotmuchError):
     pass
 class ReadOnlyDatabaseError(NotmuchError):