fix pylint

torba/basetransaction.py

@@ -150,7 +150,7 @@ class BaseInput(InputOutput):
 
     @classmethod
     def deserialize_from(cls, stream):
-        tx_ref = TXRefImmutable.from_hash(stream.read(32))
+        tx_ref = TXRefImmutable.from_hash(stream.read(32), -1)
         position = stream.read_uint32()
         script = stream.read_string()
         sequence = stream.read_uint32()

torba/hash.py

@@ -49,7 +49,11 @@ class TXRef:
 
 class TXRefImmutable(TXRef):
 
-    __slots__ = '_height',
+    __slots__ = ('_height',)
+
+    def __init__(self):
+        super().__init__()
+        self._height = -1
 
     @classmethod
     def from_hash(cls, tx_hash: bytes, height: int) -> 'TXRefImmutable':