fix new pylint warning

libagent/device/trezor.py

@@ -21,11 +21,10 @@ def _message_box(label, sp=subprocess):
     p = sp.Popen(args=args, stdin=sp.PIPE, stdout=sp.PIPE, stderr=sp.PIPE)
     out, err = p.communicate(label.encode('ascii'))
     exitcode = p.wait()
-    if exitcode == 0:
-        return out.decode('ascii')
-    else:
+    if exitcode != 0:
         log.error('UI failed: %r', err)
         raise sp.CalledProcessError(exitcode, args)
+    return out.decode('ascii')
 
 
 def _is_open_tty(stream):

libagent/formats.py

@@ -102,6 +102,8 @@ def _decompress_ed25519(pubkey):
     if pubkey[:1] == b'\x00':
         # set by Trezor fsm_msgSignIdentity() and fsm_msgGetPublicKey()
         return ed25519.VerifyingKey(pubkey[1:])
+    else:
+        return None
 
 
 def _decompress_nist256(pubkey):
@@ -126,6 +128,8 @@ def _decompress_nist256(pubkey):
         point = ecdsa.ellipticcurve.Point(curve.curve, x, y)
         return ecdsa.VerifyingKey.from_public_point(point, curve=curve,
                                                     hashfunc=hashfunc)
+    else:
+        return None
 
 
 def decompress_pubkey(pubkey, curve_name):

libagent/ssh/__init__.py

@@ -228,3 +228,4 @@ def main(device_type):
     else:
         for pk in conn.public_keys():
             sys.stdout.write(pk)
+        return 0  # success exit code

libagent/tests/test_server.py

@@ -79,9 +79,9 @@ def test_server_thread():
 
     class FakeServer(object):
         def accept(self):  # pylint: disable=no-self-use
-            if connections:
-                return connections.pop(), 'address'
-            raise socket.timeout()
+            if not connections:
+                raise socket.timeout()
+            return connections.pop(), 'address'
 
         def getsockname(self):  # pylint: disable=no-self-use
             return 'fake_server'