ssz typing now subclasses list/bytes, much easier to work with than wrapped list/bytes functionality

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

@@ -1,7 +1,7 @@
 from ..merkle_minimal import merkleize_chunks
 from ..hash_function import hash
 from .ssz_typing import (
-    SSZValue, SSZType, BasicValue, BasicType, Series, Elements, Bit, Container, List, Bytes, BytesN, uint,
+    SSZValue, SSZType, BasicValue, BasicType, Series, Elements, Bit, Container, List, Bytes, uint,
 )
 
 # SSZ Serialization
@@ -46,9 +46,8 @@ def serialize(obj: SSZValue):
 
 
 def encode_series(values: Series):
-    # bytes and bytesN are already in the right format.
-    if isinstance(values, (Bytes, BytesN)):
-        return values.items
+    if isinstance(values, bytes):  # Bytes and BytesN are already like serialized output
+        return values
 
     # Recursively serialize
     parts = [(v.type().is_fixed_size(), serialize(v)) for v in values]
@@ -84,8 +83,8 @@ def encode_series(values: Series):
 
 
 def pack(values: Series):
-    if isinstance(values, (Bytes, BytesN)):
-        return values.items
+    if isinstance(values, bytes):  # Bytes and BytesN are already packed
+        return values
     return b''.join([serialize_basic(value) for value in values])
 
 

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

@@ -188,10 +188,10 @@ class Container(Series, metaclass=SSZType):
 
 
 class ParamsBase(Series):
-    _bare = True
+    _has_params = False
 
     def __new__(cls, *args, **kwargs):
-        if cls._bare:
+        if not cls._has_params:
             raise Exception("cannot init bare type without params")
         return super().__new__(cls, **kwargs)
 
@@ -200,13 +200,13 @@ class ParamsMeta(SSZType):
 
     def __new__(cls, class_name, parents, attrs):
         out = type.__new__(cls, class_name, parents, attrs)
+        if hasattr(out, "_has_params") and getattr(out, "_has_params"):
             for k, v in attrs.items():
                 setattr(out, k, v)
         return out
 
     def __getitem__(self, params):
         o = self.__class__(self.__name__, (self,), self.attr_from_params(params))
-        o._bare = False
         return o
 
     def __str__(self):
@@ -218,7 +218,7 @@ class ParamsMeta(SSZType):
     def attr_from_params(self, p):
         # single key params are valid too. Wrap them in a tuple.
         params = p if isinstance(p, tuple) else (p,)
-        res = {}
+        res = {'_has_params': True}
         i = 0
         for (name, typ) in self.__annotations__.items():
             if hasattr(self.__class__, name):
@@ -262,13 +262,17 @@ class ElementsType(ParamsMeta):
 
 
 class Elements(ParamsBase, metaclass=ElementsType):
+    pass
+
+
+class BaseList(list, Elements):
 
     def __init__(self, *args):
         items = self.extract_args(*args)
 
         if not self.value_check(items):
             raise ValueError(f"Bad input for class {self.__class__}: {items}")
-        self.items = items
+        super().__init__(items)
 
     @classmethod
     def value_check(cls, value):
@@ -284,39 +288,32 @@ class Elements(ParamsBase, metaclass=ElementsType):
 
     def __str__(self):
         cls = self.__class__
-        return f"{cls.__name__}[{cls.elem_type.__name__}, {cls.length}]({', '.join(str(v) for v in self.items)})"
+        return f"{cls.__name__}[{cls.elem_type.__name__}, {cls.length}]({', '.join(str(v) for v in self)})"
 
     def __getitem__(self, i) -> SSZValue:
-        return self.items[i]
+        if i < 0:
+            raise IndexError(f"cannot get item in type {self.__class__} at negative index {i}")
+        if i > len(self):
+            raise IndexError(f"cannot get item in type {self.__class__}"
+                             f" at out of bounds index {i}")
+        return super().__getitem__(i)
 
     def __setitem__(self, k, v):
         if k < 0:
             raise IndexError(f"cannot set item in type {self.__class__} at negative index {k} (to {v})")
-        if k > len(self.items):
+        if k > len(self):
             raise IndexError(f"cannot set item in type {self.__class__}"
-                             f" at out of bounds index {k} (to {v}, bound: {len(self.items)})")
-        self.items[k] = coerce_type_maybe(v, self.__class__.elem_type, strict=True)
+                             f" at out of bounds index {k} (to {v}, bound: {len(self)})")
+        super().__setitem__(k, coerce_type_maybe(v, self.__class__.elem_type, strict=True))
 
     def append(self, v):
-        self.items.append(coerce_type_maybe(v, self.__class__.elem_type, strict=True))
-
-    def pop(self):
-        if len(self.items) == 0:
-            raise IndexError("Pop from empty list")
-        else:
-            return self.items.pop()
-
-    def __len__(self):
-        return len(self.items)
-
-    def __repr__(self):
-        return repr(self.items)
+        super().append(coerce_type_maybe(v, self.__class__.elem_type, strict=True))
 
     def __iter__(self) -> Iterator[SSZValue]:
-        return iter(self.items)
+        return super().__iter__()
 
 
-class List(Elements):
+class List(BaseList):
 
     @classmethod
     def default(cls):
@@ -327,7 +324,7 @@ class List(Elements):
         return False
 
 
-class Vector(Elements):
+class Vector(BaseList):
 
     @classmethod
     def value_check(cls, value):
@@ -342,27 +339,35 @@ class Vector(Elements):
     def is_fixed_size(cls):
         return cls.elem_type.is_fixed_size()
 
+    def append(self, v):
+        raise Exception("cannot modify vector length")
+
+    def pop(self, *args):
+        raise Exception("cannot modify vector length")
+
 
 class BytesType(ElementsType):
     elem_type: SSZType = byte
     length: int
 
 
-class BytesLike(Elements, metaclass=BytesType):
+class BaseBytes(bytes, Elements, metaclass=BytesType):
+
+    def __new__(cls, *args) -> "BaseBytes":
+        extracted_val = cls.extract_args(*args)
+        if not cls.value_check(extracted_val):
+            raise ValueError(f"Bad input for class {cls}: {extracted_val}")
+        return super().__new__(cls, extracted_val)
 
     @classmethod
     def extract_args(cls, *args):
-        x = list(args)
-        if len(x) == 1 and isinstance(x[0], (GeneratorType, bytes, BytesLike)):
+        x = args
+        if len(x) == 1 and isinstance(x[0], (GeneratorType, bytes)):
             x = x[0]
-        if isinstance(x, bytes):
+        if isinstance(x, bytes):  # Includes BytesLike
             return x
-        elif isinstance(x, BytesLike):
-            return x.items
-        elif isinstance(x, GeneratorType):
-            return bytes(x)
         else:
-            return bytes(x)
+            return bytes(x)  # E.g. GeneratorType put into bytes.
 
     @classmethod
     def value_check(cls, value):
@@ -374,7 +379,7 @@ class BytesLike(Elements, metaclass=BytesType):
         return f"{cls.__name__}[{cls.length}]: {self.hex()}"
 
 
-class Bytes(BytesLike):
+class Bytes(BaseBytes):
 
     @classmethod
     def default(cls):
@@ -385,7 +390,14 @@ class Bytes(BytesLike):
         return False
 
 
-class BytesN(BytesLike):
+class BytesN(BaseBytes):
+
+    @classmethod
+    def extract_args(cls, *args):
+        if len(args) == 0:
+            return cls.default()
+        else:
+            return super().extract_args(*args)
 
     @classmethod
     def default(cls):

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

@@ -211,3 +211,5 @@ def test_bytesn_subclass():
     assert issubclass(Hash, Bytes32)
 
     assert not issubclass(Bytes48, Bytes32)
+
+    assert len(Bytes32() + Bytes48()) == 80