[PATCH] python: fix error handling

[Justus Winter]

Before 3434d1940 the return values of libnotmuch functions were
declared as c_void_p and the code checking for errors compared the
returned value to None, which is the ctypes equivalent of a NULL
pointer.

But said commit wrapped all the data types in python classes and the
semantic changed in a subtle way. If a function returns NULL, the
wrapped python value is falsish, but no longer equal to None.

Backported from master to 0.11.
---
 bindings/python/notmuch/database.py |   16 ++++++++--------
 bindings/python/notmuch/filename.py |    2 +-
 bindings/python/notmuch/message.py  |    6 +++---
 bindings/python/notmuch/tag.py      |    2 +-
 bindings/python/notmuch/thread.py   |    6 +++---
 5 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/bindings/python/notmuch/database.py b/bindings/python/notmuch/database.py
index 7923f76..0074ba3 100644
--- a/bindings/python/notmuch/database.py
+++ b/bindings/python/notmuch/database.py
@@ -168,7 +168,7 @@ class Database(object):
 
         res = Database._create(_str(path), Database.MODE.READ_WRITE)
 
-        if res is None:
+        if not res:
             raise NotmuchError(
                 message="Could not create the specified database")
         self._db = res
@@ -188,7 +188,7 @@ class Database(object):
         """
         res = Database._open(_str(path), mode)
 
-        if res is None:
+        if not res:
             raise NotmuchError(message="Could not open the specified database")
         self._db = res
 
@@ -645,7 +645,7 @@ class Query(object):
         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:
+        if not query_p:
             raise NullPointerError
         self._query = query_p
 
@@ -679,7 +679,7 @@ class Query(object):
         self._assert_query_is_initialized()
         threads_p = Query._search_threads(self._query)
 
-        if threads_p is None:
+        if not threads_p:
             raise NullPointerError
         return Threads(threads_p, self)
 
@@ -693,7 +693,7 @@ class Query(object):
         self._assert_query_is_initialized()
         msgs_p = Query._search_messages(self._query)
 
-        if msgs_p is None:
+        if not msgs_p:
             raise NullPointerError
         return Messages(msgs_p, self)
 
@@ -759,7 +759,7 @@ 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:
+        if not self._dir_p:
             raise NotmuchError(STATUS.NOT_INITIALIZED)
 
     def __init__(self, path, dir_p, parent):
@@ -920,7 +920,7 @@ class Filenames(object):
     _move_to_next.restype = None
 
     def next(self):
-        if self._files_p is None:
+        if not self._files_p:
             raise NotmuchError(STATUS.NOT_INITIALIZED)
 
         if not self._valid(self._files_p):
@@ -946,7 +946,7 @@ class Filenames(object):
                      # NotmuchError(:attr:`STATUS`.NOT_INITIALIZED)
                      for file in files: print file
         """
-        if self._files_p is None:
+        if not self._files_p:
             raise NotmuchError(STATUS.NOT_INITIALIZED)
 
         i = 0
diff --git a/bindings/python/notmuch/filename.py b/bindings/python/notmuch/filename.py
index a7cd7e6..f7313ec 100644
--- a/bindings/python/notmuch/filename.py
+++ b/bindings/python/notmuch/filename.py
@@ -69,7 +69,7 @@ class Filenames(object):
              reference to it, so we can automatically delete the db object
              once all derived objects are dead.
         """
-        if files_p is None:
+        if not files_p:
             raise NotmuchError(STATUS.NULL_POINTER)
 
         self._files = files_p
diff --git a/bindings/python/notmuch/message.py b/bindings/python/notmuch/message.py
index ce8e718..5540df3 100644
--- a/bindings/python/notmuch/message.py
+++ b/bindings/python/notmuch/message.py
@@ -116,7 +116,7 @@ class Messages(object):
         :TODO: Make the iterator work more than once and cache the tags in
                the Python object.(?)
         """
-        if msgs_p is None:
+        if not msgs_p:
             raise NotmuchError(STATUS.NULL_POINTER)
 
         self._msgs = msgs_p
@@ -321,7 +321,7 @@ class Message(object):
               automatically delete the parent object once all derived
               objects are dead.
         """
-        if msg_p is None:
+        if not msg_p:
             raise NotmuchError(STATUS.NULL_POINTER)
         self._msg = msg_p
         #keep reference to parent, so we keep it alive
@@ -380,7 +380,7 @@ class Message(object):
 
         msgs_p = Message._get_replies(self._msg)
 
-        if msgs_p is None:
+        if not msgs_p:
             return None
 
         return Messages(msgs_p, self)
diff --git a/bindings/python/notmuch/tag.py b/bindings/python/notmuch/tag.py
index 2fb7d32..4881db9 100644
--- a/bindings/python/notmuch/tag.py
+++ b/bindings/python/notmuch/tag.py
@@ -70,7 +70,7 @@ class Tags(object):
         :TODO: Make the iterator optionally work more than once by
                cache the tags in the Python object(?)
         """
-        if tags_p is None:
+        if not tags_p:
             raise NotmuchError(STATUS.NULL_POINTER)
 
         self._tags = tags_p
diff --git a/bindings/python/notmuch/thread.py b/bindings/python/notmuch/thread.py
index 5058846..594fa52 100644
--- a/bindings/python/notmuch/thread.py
+++ b/bindings/python/notmuch/thread.py
@@ -97,7 +97,7 @@ class Threads(object):
         :TODO: Make the iterator work more than once and cache the tags in
                the Python object.(?)
         """
-        if threads_p is None:
+        if not threads_p:
             raise NotmuchError(STATUS.NULL_POINTER)
 
         self._threads = threads_p
@@ -227,7 +227,7 @@ class Thread(object):
               automatically delete the parent object once all derived
               objects are dead.
         """
-        if thread_p is None:
+        if not thread_p:
             raise NotmuchError(STATUS.NULL_POINTER)
         self._thread = thread_p
         #keep reference to parent, so we keep it alive
@@ -288,7 +288,7 @@ class Thread(object):
 
         msgs_p = Thread._get_toplevel_messages(self._thread)
 
-        if msgs_p is None:
+        if not msgs_p:
             raise NotmuchError(STATUS.NULL_POINTER)
 
         return Messages(msgs_p, self)
-- 
1.7.8.3