Add "no_run_validators()" context manager

docs/init.rst

@@ -251,6 +251,16 @@ And finally you can disable validators globally:
       ...
    TypeError: ("'x' must be <class 'int'> (got '128' that is a <class 'str'>).", Attribute(name='x', default=NOTHING, validator=[<instance_of validator for type <class 'int'>>, <function fits_byte at 0x10fd7a0d0>], repr=True, cmp=True, hash=True, init=True, metadata=mappingproxy({}), type=None, converter=None), <class 'int'>, '128')
 
+You can achieve the same by using the context manager:
+
+   >>> with attrs.no_run_validators():
+   ...     C("128")
+   C(x='128')
+   >>> C("128")
+   Traceback (most recent call last):
+      ...
+   TypeError: ("'x' must be <class 'int'> (got '128' that is a <class 'str'>).", Attribute(name='x', default=NOTHING, validator=[<instance_of validator for type <class 'int'>>, <function fits_byte at 0x10fd7a0d0>], repr=True, cmp=True, hash=True, init=True, metadata=mappingproxy({}), type=None, converter=None), <class 'int'>, '128')
+
 
 .. _converters:
 

src/attr/__init__.py

@@ -6,7 +6,7 @@
 
 from . import converters, exceptions, filters, setters, validators
 from ._cmp import cmp_using
-from ._config import get_run_validators, set_run_validators
+from ._config import get_run_validators, no_run_validators, set_run_validators
 from ._funcs import asdict, assoc, astuple, evolve, has, resolve_types
 from ._make import (
     NOTHING,

src/attr/__init__.pyi

@@ -3,6 +3,7 @@ import sys
 from typing import (
     Any,
     Callable,
+    ContextManager,
     Dict,
     Generic,
     List,
@@ -473,6 +474,7 @@ def evolve(inst: _T, **changes: Any) -> _T: ...
 
 def set_run_validators(run: bool) -> None: ...
 def get_run_validators() -> bool: ...
+def no_run_validators() -> ContextManager[None]: ...
 
 # aliases --
 

src/attr/_config.py

@@ -1,4 +1,5 @@
 from __future__ import absolute_import, division, print_function
+from contextlib import contextmanager
 
 
 __all__ = ["set_run_validators", "get_run_validators"]
@@ -21,3 +22,17 @@ def get_run_validators():
     Return whether or not validators are run.
     """
     return _run_validators
+
+
+@contextmanager
+def no_run_validators():
+    """
+    Context manager that disables running validators within its context.
+
+    .. versionadded:: 21.3.0
+    """
+    set_run_validators(False)
+    try:
+        yield
+    finally:
+        set_run_validators(True)

tests/test_config.py

@@ -41,3 +41,25 @@ def test_wrong_type(self):
         with pytest.raises(TypeError) as e:
             _config.set_run_validators("False")
         assert "'run' must be bool." == e.value.args[0]
+
+    def test_no_run_validators(self):
+        """
+        The `no_run_validators` context manager disables running validators,
+        but only within its context.
+        """
+        assert _config._run_validators is True
+        with _config.no_run_validators():
+            assert _config._run_validators is False
+        assert _config._run_validators is True
+
+    def test_no_run_validators_with_errors(self):
+        """
+        Running validators is re-enabled even if an error is raised.
+        """
+        assert _config._run_validators is True
+        with pytest.raises(ValueError):
+            with _config.no_run_validators():
+                assert _config._run_validators is False
+                raise ValueError("haha!")
+        assert _config._run_validators is True
+