Implement hasattr for contract events

Author: realjohnward

newsfragments/1560.bugfix.rst

@@ -0,0 +1,9 @@
+Fixed hasattr overloader method in the web3.ContractEvent class by implementing a try/except handler
+that returns False if an exception is raised in the __getattr__ overloader method 
+(since __getattr__ HAS to be called in every __hasattr__ call). 
+
+Created an Exception class called 'ABIEventFunctionNotFound', which inherits from both AttributeError and 
+MismatchedABI, and replaced the MismatchedABI raise with a raise to the created class in the __getattr__ 
+overloader method of the web3.ContractEvent object. 
+
+Created the test scripts 'test_contract_events_hasattr.py' and 'test_contract_events_getattr.py'

tests/core/contracts/test_extracting_event_data.py

@@ -12,6 +12,7 @@
     get_event_data,
 )
 from web3.exceptions import (
+    ABIEventFunctionNotFound,
     LogTopicError,
     ValidationError,
 )
@@ -113,6 +114,29 @@ def dup_txn_receipt(
     return wait_for_transaction(web3, dup_txn_hash)
 
 
+@pytest.fixture()
+def single_event_abi():
+    return '''[{"anonymous":false,"inputs":[{"indexed":false,"name":"value","type":"uint256"}],"name":"Increased","type":"event"}]'''  # noqa: E501
+
+
+def test_contract_event_getattr(web3, single_event_abi):
+    contract = web3.eth.contract(abi=single_event_abi)
+    assert getattr(contract.events, "Increased")
+
+
+def test_contract_event_getattr_raises_error(web3, single_event_abi):
+    contract = web3.eth.contract(abi=single_event_abi)
+
+    with pytest.raises(ABIEventFunctionNotFound):
+        getattr(contract.events, "Decreased")
+
+
+def test_contract_event_hasattr(web3, single_event_abi):
+    contract = web3.eth.contract(abi=single_event_abi)
+    assert hasattr(contract.events, "Increased") is True
+    assert hasattr(contract.events, "Decreased") is False
+
+
 @pytest.mark.parametrize(
     'contract_fn,event_name,call_args,expected_args',
     (

web3/contract.py

@@ -110,6 +110,7 @@
     MutableAttributeDict,
 )
 from web3.exceptions import (
+    ABIEventFunctionNotFound,
     BadFunctionCallOutput,
     BlockNumberOutofRange,
     FallbackNotFound,
@@ -239,7 +240,7 @@ def __getattr__(self, event_name: str) -> "ContractEvent":
                 "Are you sure you provided the correct contract abi?"
             )
         elif event_name not in self.__dict__['_events']:
-            raise MismatchedABI(
+            raise ABIEventFunctionNotFound(
                 "The event '{}' was not found in this contract's abi. ".format(event_name),
                 "Are you sure you provided the correct contract abi?"
             )
@@ -257,6 +258,12 @@ def __iter__(self) -> Iterable["ContractEvent"]:
         for event in self._events:
             yield self[event['name']]
 
+    def __hasattr__(self, event_name: str) -> bool:
+        try:
+            return event_name in self.__dict__['_events']
+        except ABIEventFunctionNotFound:
+            return False
+
 
 class Contract:
     """Base class for Contract proxy classes.

web3/exceptions.py

@@ -70,6 +70,14 @@ class MismatchedABI(Exception):
     pass
 
 
+class ABIEventFunctionNotFound(AttributeError, MismatchedABI):
+    """
+    Raised when an attempt is made to access an event
+    that does not exist in the ABI.
+    """
+    pass
+
+
 class FallbackNotFound(Exception):
     """
     Raised when fallback function doesn't exist in contract.