better error message

lib/commands.py

@@ -331,9 +331,9 @@ class Commands:
         """Import a private key. """
         try:
             addr = self.wallet.import_key(privkey, self.password)
-            out = "Keypair imported: ", addr
+            out = "Keypair imported: " + addr
         except Exception as e:
-            out = "Error: Keypair import failed: " + str(e)
+            out = "Error: " + str(e)
         return out
 
     def _resolver(self, x):

lib/wallet.py

@@ -291,7 +291,7 @@ class Abstract_Wallet(object):
         return account is not None
 
     def import_key(self, sec, password):
-        assert self.can_import()
+        assert self.can_import(), 'This wallet cannot import private keys'
         try:
             pubkey = public_key_from_private_key(sec)
             address = public_key_to_bc_address(pubkey.decode('hex'))