new @as_failure_raiser decorator to create a failure raiser by decorating an existing validation function. Fixes #36

Author: Sylvain MARIE

valid8/__init__.py

@@ -1,6 +1,6 @@
 from valid8.utils_typing import Boolean, is_pep484_nonable
 
-from valid8.base import Failure, WrappingFailure, failure_raiser
+from valid8.base import Failure, ValidationFailed, failure_raiser, as_failure_raiser
 from valid8.composition import CompositionFailure, AtLeastOneFailed, and_, DidNotFail, not_, AllValidatorsFailed, or_, \
     XorTooManySuccess, xor_, not_all, fail_on_none, skip_on_none
 
@@ -33,7 +33,7 @@
     # -- utils_typing
     'Boolean', 'is_pep484_nonable',
     # -- base
-    'Failure', 'ValidationFailed', 'failure_raiser',
+    'Failure', 'ValidationFailed', 'failure_raiser', 'as_failure_raiser',
     # -- composition
     'CompositionFailure', 'AtLeastOneFailed', 'and_', 'DidNotFail', 'not_', 'AllValidatorsFailed', 'or_',
     'XorTooManySuccess', 'xor_', 'not_all', 'fail_on_none', 'skip_on_none',

valid8/base.py

@@ -495,6 +495,39 @@ def raiser(x):
     return raiser
 
 
+def as_failure_raiser(failure_type=None,     # type: Type[ValidationFailed]
+                      help_msg=None,         # type: str
+                      **kw_context_args):
+    """
+    A decorator to define a failure raiser. Same functionality then `failure_raiser`:
+
+    >>> import sys, pytest
+    >>> if sys.version_info < (3, 0):
+    ...     pytest.skip('doctest skipped in python 2 because exception namespace is different but details matter')
+
+    >>> @as_failure_raiser(help_msg="x should be smaller than 4")
+    ... def is_small_with_details(x):
+    ...     return x < 4
+    >>> is_small_with_details(2)
+    >>> is_small_with_details(11)
+    Traceback (most recent call last):
+    ...
+    valid8.base.ValidationFailed: x should be smaller than 4. Function [is_small_with_details] returned [False] for
+        value 11.
+
+    :param failure_type:
+    :param help_msg:
+    :param kw_context_args:
+    :return:
+    """
+    if failure_type is None and help_msg is None and len(kw_context_args) == 0:
+        raise ValueError("at least one argument should be provided in @as_failure_raiser")
+
+    def apply_decorator(f):
+        return failure_raiser(f, failure_type=failure_type, help_msg=help_msg, **kw_context_args)
+    return apply_decorator
+
+
 class ValueIsNone(Failure, TypeError):
     help_msg = "The value must be non-None"