Use abc module to signal abstract base classes

The Completer class is abastract, and it's complete method is also
abstract. Using ABCMeta achieve two thing, first it will cause an error
if a developer doesn't overwrite the method in a subclass. And second
that it tells the static analysis tools to ignore the unused arguments
in the signature, since this is the definition of a signature, not an
actual function.

By the same logic addressbook.AddressBook, and account.Account have been
extended to use ABCMeta as their metaclass and have had their abstract
methods decorated with the abstract method attribute.

3 files changed, 16 insertions, 2 deletions

diff --git a/alot/account.py b/alot/account.py
index 912380e3..5e66e9bf 100644
--- a/alot/account.py
+++ b/alot/account.py
@@ -1,6 +1,7 @@
 # Copyright (C) 2011-2012  Patrick Totzke <patricktotzke@gmail.com>
 # This file is released under the GNU GPL, version 3 or a later revision.
 # For further details see the COPYING file
+import abc
 import glob
 import logging
 import mailbox
@@ -29,6 +30,8 @@ class Account(object):
         command to send out mails.
     """
 
+    __metaclass__ = abc.ABCMeta
+
     address = None
     """this accounts main email address"""
     aliases = []
@@ -159,6 +162,7 @@ class Account(object):
         if self.draft_box is not None:
             return self.store_mail(self.draft_box, mail)
 
+    @abc.abstractmethod
     def send_mail(self, mail):
         """
         sends given mail
@@ -168,7 +172,7 @@ class Account(object):
         :returns: a `Deferred` that errs back with a class:`SendingMailFailed`,
                   containing a reason string if an error occured.
         """
-        raise NotImplementedError
+        pass
 
 
 class SendmailAccount(Account):
diff --git a/alot/addressbook/__init__.py b/alot/addressbook/__init__.py
index 6269f5d1..da0863f4 100644
--- a/alot/addressbook/__init__.py
+++ b/alot/addressbook/__init__.py
@@ -2,6 +2,7 @@
 # This file is released under the GNU GPL, version 3 or a later revision.
 # For further details see the COPYING file
 import re
+import abc
 
 
 class AddressbookError(Exception):
@@ -17,9 +18,13 @@ class AddressBook(object):
         unspecified. See :class:`AbookAddressBook` and
         :class:`ExternalAddressbook` for implementations.
     """
+
+    __metaclass__ = abc.ABCMeta
+
     def __init__(self, ignorecase=True):
         self.reflags = re.IGNORECASE if ignorecase else 0
 
+    @abc.abstractmethod
     def get_contacts(self):
         """list all contacts tuples in this abook as (name, email) tuples"""
         return []
diff --git a/alot/completion.py b/alot/completion.py
index 314fa0c6..cb9bbad8 100644
--- a/alot/completion.py
+++ b/alot/completion.py
@@ -1,6 +1,7 @@
 # Copyright (C) 2011-2012  Patrick Totzke <patricktotzke@gmail.com>
 # This file is released under the GNU GPL, version 3 or a later revision.
 # For further details see the COPYING file
+import abc
 import argparse
 import glob
 import logging
@@ -19,6 +20,10 @@ from .errors import CompletionError
 
 class Completer(object):
     """base class for completers"""
+
+    __metaclass__ = abc.ABCMeta
+
+    @abc.abstractmethod
     def complete(self, original, pos):
         """returns a list of completions and cursor positions for the
         string original from position pos on.
@@ -32,7 +37,7 @@ class Completer(object):
         :rtype: list of (str, int)
         :raises: :exc:`CompletionError`
         """
-        return list()
+        pass
 
     def relevant_part(self, original, pos, sep=' '):
         """