[RFC] Enhancement/one of validator (#181)

CHANGELOG.rst

@@ -52,6 +52,9 @@ Changes:
   `#128 <https://github.com/python-attrs/attrs/pull/128>`_
 - ``__attrs_post_init__()`` is now run if validation is disabled.
   `#130 <https://github.com/python-attrs/attrs/pull/130>`_
+- Added `attr.validators.in_(options)`` that, given the allowed `options`, checks whether the attribute value is in it.
+  This can be used to check constants, enums, mappings, etc.
+  `#181 <https://github.com/python-attrs/attrs/pull/181>`_
 - Added ``attr.validators.and_()`` that composes multiple validators into one.
   `#161 <https://github.com/python-attrs/attrs/issues/161>`_
 - For convenience, the ``validator`` argument of ``@attr.s`` now can take a ``list`` of validators that are wrapped using ``and_()``.

docs/api.rst

@@ -270,6 +270,33 @@ Validators
          ...
       TypeError: ("'x' must be <type 'int'> (got None that is a <type 'NoneType'>).", Attribute(name='x', default=NOTHING, validator=<instance_of validator for type <type 'int'>>, repr=True, cmp=True, hash=None, init=True), <type 'int'>, None)
 
+.. autofunction:: attr.validators.in_
+
+   For example:
+
+   .. doctest::
+
+       >>> import enum
+       >>> class State(enum.Enum):
+       ...     ON = "on"
+       ...     OFF = "off"
+       >>> @attr.s
+       ... class C(object):
+       ...     state = attr.ib(validator=attr.validators.in_(State))
+       ...     val = attr.ib(validator=attr.validators.in_([1, 2, 3]))
+       >>> C(State.ON, 1)
+       C(state=<State.ON: 'on'>, val=1)
+       >>> C("on", 1)
+       Traceback (most recent call last):
+          ...
+       ValueError: 'state' must be in <enum 'State'> (got 'on')
+       >>> C(State.ON, 4)
+       Traceback (most recent call last):
+          ...
+       ValueError: 'val' must be in [1, 2, 3] (got 4)
+
+.. autofunction:: attr.validators.provides
+
 .. autofunction:: attr.validators.and_
 
    For convenience, it's also possible to pass a list to :func:`attr.ib`'s validator argument.
@@ -279,8 +306,6 @@ Validators
       x = attr.ib(validator=attr.validators.and_(v1, v2, v3))
       x = attr.ib(validator=[v1, v2, v3])
 
-.. autofunction:: attr.validators.provides
-
 .. autofunction:: attr.validators.optional
 
    For example:

src/attr/validators.py

@@ -48,9 +48,9 @@ def instance_of(type):
     :param type: The type to check for.
     :type type: type or tuple of types
 
-    The :exc:`TypeError` is raised with a human readable error message, the
-    attribute (of type :class:`attr.Attribute`), the expected type, and the
-    value it got.
+    :raises TypeError: With a human readable error message, the attribute
+        (of type :class:`attr.Attribute`), the expected type, and the value it
+        got.
     """
     return _InstanceOfValidator(type)
 
@@ -87,9 +87,9 @@ def provides(interface):
 
     :param zope.interface.Interface interface: The interface to check for.
 
-    The :exc:`TypeError` is raised with a human readable error message, the
-    attribute (of type :class:`attr.Attribute`), the expected interface, and
-    the value it got.
+    :raises TypeError: With a human readable error message, the attribute
+        (of type :class:`attr.Attribute`), the expected interface, and the
+        value it got.
     """
     return _ProvidesValidator(interface)
 
@@ -127,3 +127,39 @@ def optional(validator):
     if isinstance(validator, list):
         return _OptionalValidator(_AndValidator(validator))
     return _OptionalValidator(validator)
+
+
+@attributes(repr=False, slots=True)
+class _InValidator(object):
+    options = attr()
+
+    def __call__(self, inst, attr, value):
+        if value not in self.options:
+            raise ValueError(
+                "'{name}' must be in {options!r} (got {value!r})"
+                .format(name=attr.name, options=self.options, value=value)
+            )
+
+    def __repr__(self):
+        return (
+            "<in_ validator with options {options!r}>"
+            .format(options=self.options)
+        )
+
+
+def in_(options):
+    """
+    A validator that raises a :exc:`ValueError` if the initializer is called
+    with a value that does not belong in the options provided.  The check is
+    performed using ``value in options``.
+
+    :param options: Allowed options.
+    :type options: list, tuple, :class:`enum.Enum`, ...
+
+    :raises ValueError: With a human readable error message, the attribute (of
+       type :class:`attr.Attribute`), the expected options, and the value it
+       got.
+
+    .. versionadded:: 17.1.0
+    """
+    return _InValidator(options)

tests/test_validators.py

@@ -7,7 +7,7 @@
 import pytest
 import zope.interface
 
-from attr.validators import and_, instance_of, provides, optional
+from attr.validators import and_, instance_of, provides, optional, in_
 from attr._compat import TYPE
 from attr._make import attributes, attr
 
@@ -214,3 +214,37 @@ def test_repr(self, validator):
                  "<{type} 'int'>> or None>")
                 .format(type=TYPE)
             ) == repr(v)
+
+
+class TestIn_(object):
+    """
+    Tests for `in_`.
+    """
+    def test_success_with_value(self):
+        """
+        If the value is in our options, nothing happens.
+        """
+        v = in_([1, 2, 3])
+        a = simple_attr("test")
+        v(1, a, 3)
+
+    def test_fail(self):
+        """
+        Raise ValueError if the value is outside our options.
+        """
+        v = in_([1, 2, 3])
+        a = simple_attr("test")
+        with pytest.raises(ValueError) as e:
+            v(None, a, None)
+        assert (
+            "'test' must be in [1, 2, 3] (got None)",
+        ) == e.value.args
+
+    def test_repr(self):
+        """
+        Returned validator has a useful `__repr__`.
+        """
+        v = in_([3, 4, 5])
+        assert(
+            ("<in_ validator with options [3, 4, 5]>")
+        ) == repr(v)