Merge 5522b15 into bc5ef6e

deal/_decorators/__init__.py

@@ -4,6 +4,7 @@
 from .post import Post
 from .pre import Pre
 from .raises import Raises
+from .reason import Reason
 from .silent import Silent
 
 
@@ -14,5 +15,6 @@
     'Post',
     'Pre',
     'Raises',
+    'Reason',
     'Silent',
 ]

deal/_decorators/reason.py

@@ -0,0 +1,35 @@
+from typing import Callable
+
+from .base import Base
+from .._types import ExceptionType
+from .._exceptions import ReasonContractError
+
+
+class Reason(Base):
+    exception: ExceptionType = ReasonContractError
+
+    def __init__(self, trigger: Exception, validator: Callable, *,
+                 message: str = None, exception: ExceptionType = None, debug: bool = False):
+        """
+        Step 1. Set allowed exceptions list.
+        """
+        self.trigger = trigger
+        super().__init__(
+            validator=validator,
+            message=message,
+            exception=exception,
+            debug=debug,
+        )
+
+    def patched_function(self, *args, **kwargs):
+        """
+        Step 3. Wrapped function calling.
+        """
+        try:
+            return self.function(*args, **kwargs)
+        except self.trigger as origin:
+            try:
+                self.validate(*args, **kwargs)
+            except self.exception:
+                raise self.exception from origin
+            raise

deal/_exceptions.py

@@ -20,6 +20,10 @@ class RaisesContractError(ContractError):
     pass
 
 
+class ReasonContractError(ContractError):
+    pass
+
+
 class OfflineContractError(ContractError):
     pass