attrs/attr/validators.py

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2015-01-29 11:20:17 +00:00
# -*- coding: utf-8 -*-
from __future__ import absolute_import, division, print_function
class InstanceValidator(object):
# We use a callable class to be able to change the ``__repr__``.
def __init__(self, type_):
self.type_ = type_
def __call__(self, attr, value):
if not isinstance(value, self.type_):
raise TypeError(
"'{name}' must be {type!r} (got {value!r} that is a "
"{actual!r})."
.format(name=attr.name, type=self.type_,
actual=value.__class__, value=value),
attr, self.type_, value,
)
def __repr__(self):
return (
"<instance_of validator for type {type!r}>"
.format(type=self.type_)
)
def instance_of(type_):
"""
A validator that raises a :exc:`TypeError` if the initializer is called
with a wrong type for this particular attribute (checks are perfomed using
:func:`isinstance`).
:param type_: The type to check for.
:type type_: type
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.
"""
return InstanceValidator(type_)