Implemented "Modify Word Length"

Closes #29 (closed)

Port.InputPort has a new property value_length that describes the word length of the input on the operation related to that port.

Port.InputPort.signal and its abstract function has been removed according to the class diagram.01_-Swords_and_Sandals_Classic_Collection-_Title_Theme

b_asic/port.py

@@ -35,15 +35,6 @@ class Port(ABC):
         """Return a list of all connected signals."""
         raise NotImplementedError
 
-    @abstractmethod
-    def signal(self, i: int = 0) -> Signal:
-        """Return the connected signal at index i.
-
-        Keyword argumens:
-        i: integer index of the signal requsted.
-        """
-        raise NotImplementedError
-
     @property
     @abstractmethod
     def connected_ports(self) -> List["Port"]:
@@ -119,24 +110,32 @@ class InputPort(AbstractPort):
     """
 
     _source_signal: Optional[Signal]
+    _value_length: Optional[int]
+
 
     def __init__(self, port_id: PortIndex, operation: Operation):
         super().__init__(port_id, operation)
         self._source_signal = None
+        self._value_length = None
 
     @property
     def signals(self) -> List[Signal]:
         return [] if self._source_signal is None else [self._source_signal]
 
-    def signal(self, i: int = 0) -> Signal:
-        assert 0 <= i < self.signal_count(), "Signal index out of bound."
-        assert self._source_signal is not None, "No Signal connect to InputPort."
-        return self._source_signal
+    @property
+    def value_length(self) -> Optional[int]:
+        return self._value_length
 
     @property
     def connected_ports(self) -> List[Port]:
         return [] if self._source_signal is None or self._source_signal.source is None \
             else [self._source_signal.source]
+  
+    @value_length.setter
+    def value_length(self, bits: Optional[int]) -> None:
+        assert isinstance(bits, int) or bits is None, "Value length on input port has to be of type Int or NoneType."
+        assert bits is None or bits >= 0, "Value length on input port has to be a non-negative integer or None."
+        self._value_length = bits
 
     def signal_count(self) -> int:
         return 0 if self._source_signal is None else 1