use as_bytes function to reduce code duplication, and for later usage

test_libs/pyspec/eth2spec/utils/ssz/ssz_impl.py

@@ -41,15 +41,13 @@ def serialize(obj: SSZValue):
     if isinstance(obj, BasicValue):
         return serialize_basic(obj)
     elif isinstance(obj, Bitvector):
-        as_bytearray = [0] * ((len(obj) + 7) // 8)
-        for i in range(len(obj)):
-            as_bytearray[i // 8] |= obj[i] << (i % 8)
-        return bytes(as_bytearray)
+        return obj.as_bytes()
     elif isinstance(obj, Bitlist):
-        as_bytearray = [0] * (len(obj) // 8 + 1)
-        for i in range(len(obj)):
-            as_bytearray[i // 8] |= obj[i] << (i % 8)
-        as_bytearray[len(obj) // 8] |= 1 << (len(obj) % 8)
+        as_bytearray = list(obj.as_bytes())
+        if len(obj) % 8 == 0:
+            as_bytearray.append(1)
+        else:
+            as_bytearray[len(obj) // 8] |= 1 << (len(obj) % 8)
         return bytes(as_bytearray)
     elif isinstance(obj, Series):
         return encode_series(obj)
@@ -97,11 +95,10 @@ def encode_series(values: Series):
 def pack(values: Series):
     if isinstance(values, bytes):  # Bytes and BytesN are already packed
         return values
-    elif isinstance(values, (Bitvector, Bitlist)):
-        as_bytearray = [0] * ((len(values) + 7) // 8)
-        for i in range(len(values)):
-            as_bytearray[i // 8] |= values[i] << (i % 8)
-        return bytes(as_bytearray)
+    elif isinstance(values, Bits):
+        # packs the bits in bytes, left-aligned.
+        # Exclusive length delimiting bits for bitlists.
+        return values.as_bytes()
     return b''.join([serialize_basic(value) for value in values])
 
 

test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py

@@ -354,7 +354,12 @@ class BitElementsType(ElementsType):
 
 
 class Bits(BaseList, metaclass=BitElementsType):
-    pass
+
+    def as_bytes(self):
+        as_bytearray = [0] * ((len(self) + 7) // 8)
+        for i in range(len(self)):
+            as_bytearray[i // 8] |= int(self[i]) << (i % 8)
+        return bytes(as_bytearray)
 
 
 class Bitlist(Bits):