base_fee from None to exception pre-1559

Author: carver

eth/rlp/headers.py

@@ -1,5 +1,4 @@
 from typing import (
-    Optional,
     cast,
     overload,
 )
@@ -177,5 +176,5 @@ def is_genesis(self) -> bool:
         return self.parent_hash == GENESIS_PARENT_HASH and self.block_number == 0
 
     @property
-    def base_fee_per_gas(self) -> Optional[int]:
-        return None
+    def base_fee_per_gas(self) -> int:
+        raise AttributeError("Base fee per gas not available until London fork")

eth/vm/base.py

@@ -173,16 +173,29 @@ def create_execution_context(cls,
                                  prev_hashes: Iterable[Hash32],
                                  chain_context: ChainContextAPI) -> ExecutionContextAPI:
         fee_recipient = cls.consensus_class.get_fee_recipient(header)
-        return ExecutionContext(
-            coinbase=fee_recipient,
-            timestamp=header.timestamp,
-            block_number=header.block_number,
-            difficulty=header.difficulty,
-            gas_limit=header.gas_limit,
-            prev_hashes=prev_hashes,
-            chain_id=chain_context.chain_id,
-            base_fee_per_gas=header.base_fee_per_gas,
-        )
+        try:
+            base_fee = header.base_fee_per_gas
+        except AttributeError:
+            return ExecutionContext(
+                coinbase=fee_recipient,
+                timestamp=header.timestamp,
+                block_number=header.block_number,
+                difficulty=header.difficulty,
+                gas_limit=header.gas_limit,
+                prev_hashes=prev_hashes,
+                chain_id=chain_context.chain_id,
+            )
+        else:
+            return ExecutionContext(
+                coinbase=fee_recipient,
+                timestamp=header.timestamp,
+                block_number=header.block_number,
+                difficulty=header.difficulty,
+                gas_limit=header.gas_limit,
+                prev_hashes=prev_hashes,
+                chain_id=chain_context.chain_id,
+                base_fee_per_gas=base_fee,
+            )
 
     def execute_bytecode(self,
                          origin: Address,
@@ -673,10 +686,10 @@ def in_costless_state(self) -> Iterator[StateAPI]:
         temp_block = self.generate_block_from_parent_header_and_coinbase(header, header.coinbase)
         prev_hashes = itertools.chain((header.hash,), self.previous_hashes)
 
-        if temp_block.header.base_fee_per_gas is None:
-            free_header = temp_block.header
-        else:
+        if hasattr(temp_block.header, 'base_fee_per_gas'):
             free_header = temp_block.header.copy(base_fee_per_gas=0)
+        else:
+            free_header = temp_block.header
 
         state = self.build_state(self.chaindb.db,
                                  free_header,

eth/vm/execution_context.py

@@ -33,7 +33,7 @@ def __init__(
             gas_limit: int,
             prev_hashes: Iterable[Hash32],
             chain_id: int,
-            base_fee_per_gas: Optional[int]) -> None:
+            base_fee_per_gas: Optional[int] = None) -> None:
         self._coinbase = coinbase
         self._timestamp = timestamp
         self._block_number = block_number

eth/vm/forks/london/__init__.py

@@ -42,7 +42,7 @@ def validate_gas(
             header: BlockHeaderAPI,
             parent_header: BlockHeaderAPI) -> None:
 
-        if parent_header.base_fee_per_gas is not None:
+        if hasattr(parent_header, 'base_fee_per_gas'):
             # Follow normal gas limit rules if the previous block had a base fee
             parent_gas_limit = parent_header.gas_limit
         else:

eth/vm/forks/london/headers.py

@@ -34,13 +34,13 @@
 def calculate_expected_base_fee_per_gas(parent_header: BlockHeaderAPI) -> int:
     if parent_header is None:
         # Parent is empty when making the genesis header
-        parent_base_fee_per_gas = None
-    else:
-        parent_base_fee_per_gas = parent_header.base_fee_per_gas
-
-    if parent_base_fee_per_gas is None:
-        # Parent is a non-London header or this is a genesis header
         return INITIAL_BASE_FEE
+    else:
+        try:
+            parent_base_fee_per_gas = parent_header.base_fee_per_gas
+        except AttributeError:
+            # Parent is a non-London header
+            return INITIAL_BASE_FEE
 
     parent_gas_target = parent_header.gas_limit
     parent_gas_used = parent_header.gas_used
@@ -72,7 +72,7 @@ def create_header_from_parent(difficulty_fn: Callable[[BlockHeaderAPI, int], int
                               **header_params: Any) -> BlockHeaderAPI:
 
     if 'gas_limit' not in header_params:
-        if parent_header is not None and parent_header.base_fee_per_gas is None:
+        if parent_header is not None and not hasattr(parent_header, 'base_fee_per_gas'):
             # If the previous block was not a London block,
             #   double the gas limit, so the new target is the old gas limit
             header_params['gas_limit'] = parent_header.gas_limit * ELASTICITY_MULTIPLIER