old_contents: from __future__ import absolute_import, division, print_function
  
  
  class FrozenError(AttributeError):
      """
      A frozen/immutable instance or attribute haave been attempted to be
      modified.
  
      It mirrors the behavior of ``namedtuples`` by using the same error message
      and subclassing `AttributeError`.
  
      .. versionadded:: 20.1.0
      """
  
      msg = "can't set attribute"
      args = [msg]
  
  
  class FrozenInstanceError(FrozenError):
      """
      A frozen instance has been attempted to be modified.
  
      .. versionadded:: 16.1.0
      """
  
  
  class FrozenAttributeError(FrozenError):
      """
      A frozen attribute has been attempted to be modified.
  
      .. versionadded:: 20.1.0
      """
  
  
  class AttrsAttributeNotFoundError(ValueError):
      """
      An ``attrs`` function couldn't find an attribute that the user asked for.
  
      .. versionadded:: 16.2.0
      """
  
  
  class NotAnAttrsClassError(ValueError):
      """
      A non-``attrs`` class has been passed into an ``attrs`` function.
  
      .. versionadded:: 16.2.0
      """
  
  
  class DefaultAlreadySetError(RuntimeError):
      """
      A default has been set using ``attr.ib()`` and is attempted to be reset
      using the decorator.
  
      .. versionadded:: 17.1.0
      """
  
  
  class UnannotatedAttributeError(RuntimeError):
      """
      A class with ``auto_attribs=True`` has an ``attr.ib()`` without a type
      annotation.
  
      .. versionadded:: 17.3.0
      """
  
  
  class PythonTooOldError(RuntimeError):
      """
      It was attempted to use an ``attrs`` feature that requires a newer Python
      version.
  
      .. versionadded:: 18.2.0
      """
  
  
  class NotCallableError(TypeError):
      """
      A ``attr.ib()`` requiring a callable has been set with a value
      that is not callable.
  
      .. versionadded:: 19.2.0
      """
  
      def __init__(self, msg, value):
          super(TypeError, self).__init__(msg, value)
          self.msg = msg
          self.value = value
  
      def __str__(self):
          return str(self.msg)
  
new_contents: from __future__ import absolute_import, division, print_function
  
  
  class FrozenError(AttributeError):
      """
      A frozen/immutable instance or attribute have been attempted to be
      modified.
  
      It mirrors the behavior of ``namedtuples`` by using the same error message
      and subclassing `AttributeError`.
  
      .. versionadded:: 20.1.0
      """
  
      msg = "can't set attribute"
      args = [msg]
  
  
  class FrozenInstanceError(FrozenError):
      """
      A frozen instance has been attempted to be modified.
  
      .. versionadded:: 16.1.0
      """
  
  
  class FrozenAttributeError(FrozenError):
      """
      A frozen attribute has been attempted to be modified.
  
      .. versionadded:: 20.1.0
      """
  
  
  class AttrsAttributeNotFoundError(ValueError):
      """
      An ``attrs`` function couldn't find an attribute that the user asked for.
  
      .. versionadded:: 16.2.0
      """
  
  
  class NotAnAttrsClassError(ValueError):
      """
      A non-``attrs`` class has been passed into an ``attrs`` function.
  
      .. versionadded:: 16.2.0
      """
  
  
  class DefaultAlreadySetError(RuntimeError):
      """
      A default has been set using ``attr.ib()`` and is attempted to be reset
      using the decorator.
  
      .. versionadded:: 17.1.0
      """
  
  
  class UnannotatedAttributeError(RuntimeError):
      """
      A class with ``auto_attribs=True`` has an ``attr.ib()`` without a type
      annotation.
  
      .. versionadded:: 17.3.0
      """
  
  
  class PythonTooOldError(RuntimeError):
      """
      It was attempted to use an ``attrs`` feature that requires a newer Python
      version.
  
      .. versionadded:: 18.2.0
      """
  
  
  class NotCallableError(TypeError):
      """
      A ``attr.ib()`` requiring a callable has been set with a value
      that is not callable.
  
      .. versionadded:: 19.2.0
      """
  
      def __init__(self, msg, value):
          super(TypeError, self).__init__(msg, value)
          self.msg = msg
          self.value = value
  
      def __str__(self):
          return str(self.msg)
  
subject: fix typo (#797)