Add attr.valid

attr/__init__.py

@@ -7,6 +7,7 @@ from ._funcs import (
     assoc,
     fields,
     has,
+    valid,
 )
 from ._make import (
     Attribute,
@@ -40,5 +41,6 @@ __all__ = [
     "ib",
     "make_class",
     "s",
+    "valid",
     "validators",
 ]

attr/_funcs.py

@@ -92,3 +92,15 @@ def assoc(inst, **changes):
             )
         setattr(new, k, v)
     return new
+
+
+def valid(inst):
+    """
+    Validate all attributes on *inst* that have a validator.
+
+    Leaves all exceptions through.
+
+    :param inst: Instance of a class with ``attrs`` attributes.
+    """
+    for a in fields(inst.__class__):
+        a.validator(a, getattr(inst, a.name))

docs/api.rst

@@ -150,6 +150,23 @@ Helpers
       False
 
 
+.. autofunction:: valid
+
+   For example:
+
+   .. doctest::
+
+      >>> @attr.s
+      ... class C(object):
+      ...     x = attr.ib(validator=attr.validators.instance_of(int))
+      >>> i = C(1)
+      >>> i.x = "1"
+      >>> attr.valid(i)
+      Traceback (most recent call last):
+         ...
+      TypeError: ("'x' must be <type 'int'> (got '1' that is a <type 'str'>).", Attribute(name='x', default=NOTHING, validator=<instance_of validator for type <type 'int'>>, no_repr=False, no_cmp=False, no_hash=False, no_init=False), <type 'int'>, '1')
+
+
 .. _api_validators:
 
 Validators

docs/examples.rst

@@ -120,6 +120,17 @@ If the value does not pass the validator's standards, it just raises an appropri
       ...
    ValueError: 'x' has to be smaller than 5!
 
+``attrs`` won't intercept your changes to those attributes but you can always call :func:``attr.valid`` on any instance to verify, that it's still valid:
+
+.. doctest::
+
+   >>> i = C(4)
+   >>> i.x = 5  # works, no magic here
+   >>> attr.valid(i)
+   Traceback (most recent call last):
+      ...
+   ValueError: 'x' has to be smaller than 5!
+
 ``attrs`` ships with a bunch of validators, make sure to :ref:`check them out <api_validators>` before writing your own:
 
 .. doctest::

tests/test_funcs.py

@@ -13,11 +13,13 @@ from attr._funcs import (
     assoc,
     fields,
     has,
+    valid,
 )
 from attr._make import (
     Attribute,
     attr,
     attributes,
+    make_class,
 )
 
 
@@ -167,3 +169,30 @@ class TestAssoc(object):
         assert (
             "y is not an attrs attribute on {cl!r}.".format(cl=C),
         ) == e.value.args
+
+
+class TestValid(object):
+    """
+    Tests for `valid`.
+    """
+    def test_success(self):
+        """
+        If the validator suceeds, nothing gets raised.
+        """
+        C = make_class("C", {"x": attr(validator=lambda _, __: None)})
+        valid(C(1))
+
+    def test_propagates(self):
+        """
+        The exception of the validator is handed through.
+        """
+        def raiser(_, value):
+            if value == 42:
+                raise FloatingPointError
+
+        C = make_class("C", {"x": attr(validator=raiser)})
+        i = C(1)
+        i.x = 42
+
+        with pytest.raises(FloatingPointError):
+            valid(i)