Fix a few lint issues

libagent/gpg/__init__.py

@@ -87,7 +87,7 @@ def verify_gpg_version():
     msg = 'Existing GnuPG has version "{}" ({} required)'.format(existing_gpg,
                                                                  required_gpg)
     if not semver.match(existing_gpg, required_gpg):
-        log.error('Your GnuPG version may be incompatible: %s', existing_gpg)
+        log.error(msg)
 
 
 def check_output(args):
@@ -205,10 +205,11 @@ def run_unlock(device_type, args):
 
 
 def _server_from_assuan_fd(env):
-    fd = os.environ.get('_assuan_connection_fd')
-    if fd is not None:
-        log.info('using fd=%r for UNIX socket server', fd)
-        return server.unix_domain_socket_server_from_fd(int(fd))
+    fd = env.get('_assuan_connection_fd')
+    if fd is None:
+        return None
+    log.info('using fd=%r for UNIX socket server', fd)
+    return server.unix_domain_socket_server_from_fd(int(fd))
 
 
 def _server_from_sock_path(env):

libagent/server.py

@@ -40,31 +40,39 @@ def unix_domain_socket_server(sock_path):
 
 
 class FDServer(object):
+    """File-descriptor based server (for NeoPG)."""
+
     def __init__(self, fd):
+        """C-tor."""
         self.fd = fd
         self.sock = socket.fromfd(fd, socket.AF_UNIX, socket.SOCK_STREAM)
 
     def accept(self):
+        """Use the same socket for I/O."""
         return self, None
 
     def recv(self, n):
+        """Forward to underlying socket."""
         return self.sock.recv(n)
 
     def sendall(self, data):
+        """Forward to underlying socket."""
         return self.sock.sendall(data)
 
     def close(self):
-        pass
+        """Not needed."""
 
     def settimeout(self, _):
-        pass
+        """Not needed."""
 
     def getsockname(self):
+        """Simple representation."""
         return '<fd: {}>'.format(self.fd)
 
 
 @contextlib.contextmanager
 def unix_domain_socket_server_from_fd(fd):
+    """Build UDS-based socket server from a file descriptor."""
     yield FDServer(fd)