Use slightly faster datastructures for CodeStream internally.

Author: jacqueswww

eth/vm/code_stream.py

@@ -15,20 +15,24 @@
 class CodeStream(object):
     stream = None
     depth_processed = None
+    _len = None
+    _value = None
 
     logger = logging.getLogger('eth.vm.CodeStream')
 
     def __init__(self, code_bytes: bytes) -> None:
         validate_is_bytes(code_bytes, title="CodeStream bytes")
         self.stream = io.BytesIO(code_bytes)
+        self._value = code_bytes
+        self._len = len(code_bytes)
         self.invalid_positions = set()  # type: Set[int]
         self.depth_processed = 0
 
     def read(self, size: int) -> bytes:
         return self.stream.read(size)
 
     def __len__(self) -> int:
-        return len(self.stream.getvalue())
+        return self._len
 
     def __iter__(self) -> 'CodeStream':
         return self
@@ -37,7 +41,7 @@ def __next__(self) -> int:
         return self.next()
 
     def __getitem__(self, i: int) -> int:
-        return self.stream.getvalue()[i]
+        return self._value[i]
 
     def next(self) -> int:
         next_opcode_as_byte = self.read(1)