Merge 6e72ab4 into bad6707

deal/__init__.py

@@ -21,7 +21,10 @@
 
 
 # app
-from ._aliases import chain, ensure, inv, invariant, offline, post, pre, pure, raises, require, safe, silent
+from ._aliases import (
+    chain, ensure, inv, invariant, offline, post,
+    pre, pure, raises, reason, require, safe, silent
+)
 from ._exceptions import *  # noQA
 from ._schemes import Scheme
 from ._state import reset, switch
@@ -39,15 +42,16 @@
     'chain',
     'ensure',
     'inv',
-    'invariant',
     'offline',
     'post',
     'pre',
     'pure',
     'raises',
+    'reason',
     'safe',
     'silent',
 
     # aliases
+    'invariant',
     'require',
 ]

deal/_aliases.py

@@ -3,15 +3,16 @@
 from typing import Callable
 
 # app
-from ._decorators import Ensure, Invariant, Offline, Post, Pre, Raises, Silent
+from . import _decorators
 from ._types import ExceptionType
 
 
-require = pre = Pre
-post = Post
-ensure = Ensure
-inv = invariant = Invariant
-raises = Raises
+require = pre = _decorators.Pre
+post = _decorators.Post
+ensure = _decorators.Ensure
+inv = invariant = _decorators.Invariant
+raises = _decorators.Raises
+reason = _decorators.Reason
 
 
 # makes braces for decorator are optional
@@ -22,9 +23,9 @@ def _optional(_contract, _func: Callable = None, *, message: str = None,
     return _contract(message=message, exception=exception, debug=debug)
 
 
-offline = partial(_optional, Offline)
-safe = partial(_optional, Raises)
-silent = partial(_optional, Silent)
+offline = partial(_optional, _decorators.Offline)
+safe = partial(_optional, _decorators.Raises)
+silent = partial(_optional, _decorators.Silent)
 
 
 def chain(*contracts) -> Callable[[Callable], Callable]:

deal/_decorators/__init__.py

@@ -5,6 +5,7 @@
 from .post import Post
 from .pre import Pre
 from .raises import Raises
+from .reason import Reason
 from .silent import Silent
 
 
@@ -15,5 +16,6 @@
     'Post',
     'Pre',
     'Raises',
+    'Reason',
     'Silent',
 ]

deal/_decorators/reason.py

@@ -0,0 +1,37 @@
+# built-in
+from typing import Callable
+
+# app
+from .._exceptions import ReasonContractError
+from .._types import ExceptionType
+from .base import Base
+
+
+class Reason(Base):
+    exception: ExceptionType = ReasonContractError
+
+    def __init__(self, event: Exception, validator: Callable, *,
+                 message: str = None, exception: ExceptionType = None, debug: bool = False):
+        """
+        Step 1. Set allowed exceptions list.
+        """
+        self.event = event
+        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.event 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
 

pyproject.toml

@@ -21,7 +21,7 @@ command = "sphinx-build -M html docs docs/build"
 
 
 [tool.isort]
-line_length = 120
+line_length = 90
 combine_as_imports = true
 balanced_wrapping = true
 lines_after_imports = 2

tests/test_reason.py

@@ -0,0 +1,28 @@
+import pytest
+
+import deal
+
+
+@deal.reason(ValueError, lambda x: x == 1)
+def func(x):
+    if x == 0:
+        raise ZeroDivisionError
+    if x == 1:
+        raise ValueError
+    if x == 2:
+        raise ValueError
+    return x
+
+
+def test_reason_just_works():
+    assert func(3) == 3
+
+
+@pytest.mark.parametrize('value, exc', [
+    (0, ZeroDivisionError),
+    (1, ValueError),
+    (2, deal.ReasonContractError),
+])
+def test_reason_exception(value, exc):
+    with pytest.raises(exc):
+        func(value)