python: cleanup imports

Drop unused imports, and avoid warning about unused imports when we
import something on behalf of another module.

Signed-off-by: Justus Winter <4winter@informatik.uni-hamburg.de>

bindings/python/notmuch/compat.py

@@ -65,3 +65,7 @@ else:
             raise TypeError('Expected str, got %s' % type(value))
 
         return value.encode('utf-8', 'replace')
+
+# We import the SafeConfigParser class on behalf of other code to cope
+# with the differences between Python 2 and 3.
+SafeConfigParser # avoid warning about unused import

bindings/python/notmuch/database.py

@@ -36,7 +36,6 @@ from .errors import (
     NotmuchError,
     NullPointerError,
     NotInitializedError,
-    ReadOnlyDatabaseError,
 )
 from .message import Message
 from .tag import Tags

bindings/python/notmuch/filenames.py

@@ -19,7 +19,6 @@ Copyright 2010 Sebastian Spaeth <Sebastian@SSpaeth.de>
 from ctypes import c_char_p
 from .globals import (
     nmlib,
-    NotmuchMessageP,
     NotmuchFilenamesP,
     Python3StringMixIn,
 )

bindings/python/notmuch/globals.py

@@ -33,6 +33,11 @@ except:
 
 from .compat import Python3StringMixIn, encode_utf8 as _str
 
+# We import these on behalf of other modules.  Silence warning about
+# these symbols not being used.
+Python3StringMixIn
+_str
+
 class Enum(object):
     """Provides ENUMS as "code=Enum(['a','b','c'])" where code.a=0 etc..."""
     def __init__(self, names):