models: Add fields for supporting validation of models
Feature makes use of python descriptors to hook in type checking and other validation when fields get set.
This commit is contained in:
Thomas Adamcik
parent
5c0430ef4a
commit
07912e1091
121
mopidy/models.py
121
mopidy/models.py
@ -2,6 +2,127 @@ from __future__ import absolute_import, unicode_literals
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import json
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# TODO: split into base models, serialization and fields?
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class Field(object):
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def __init__(self, default=None, type=None, choices=None):
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"""
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Base field for use in :class:`ImmutableObject`. These fields are
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responsible type checking and other data sanitation in our models.
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For simplicity fields use the Python descriptor protocol to store the
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values in the instance dictionary. Also note that fields are mutable if
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the object they are attached to allow it.
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Default values will be validated with the exception of :class:`None`.
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:param default: default value for field
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:param type: if set the field value must be of this type
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:param choices: if set the field value must be one of these
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"""
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self._name = None # Set by FieldMeta
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self._choices = choices
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self._default = default
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self._type = type
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if self._default is not None:
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self.validate(self._default)
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def validate(self, value):
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"""Validate and possibly modify the field value before assignment"""
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if self._type and not isinstance(value, self._type):
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raise TypeError('Expected %s to be a %s, not %r' %
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(self._name, self._type, value))
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if self._choices and value not in self._choices:
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raise TypeError('Expected %s to be a one of %s, not %r' %
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(self._name, self._choices, value))
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return value
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def __get__(self, instance, owner):
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if not instance:
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return self
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return instance.__dict__.get(self._name, self._default)
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def __set__(self, instance, value):
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if value is None:
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value = self._default
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value = self.validate(value)
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if value is not None:
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instance.__dict__[self._name] = value
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else:
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self.__delete__(instance)
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def __delete__(self, instance):
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instance.__dict__.pop(self._name, None)
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class String(Field):
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def __init__(self, default=None):
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"""
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Specialized :class:`Field` which is wired up for bytes and unicode.
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:param default: default value for field
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"""
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# TODO: normalize to unicode?
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# TODO: only allow unicode?
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# TODO: disallow empty strings?
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super(String, self).__init__(type=basestring, default=default)
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class Integer(Field):
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def __init__(self, default=None, min=None, max=None):
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"""
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:class:`Field` for storing integer numbers.
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:param default: default value for field
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:param min: if set the field value larger or equal to this value
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:param max: if set the field value smaller or equal to this value
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"""
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self._min = min
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self._max = max
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super(Integer, self).__init__(type=(int, long), default=default)
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def validate(self, value):
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value = super(Integer, self).validate(value)
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if self._min is not None and value < self._min:
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raise ValueError('Expected %s to be at least %d, not %d' %
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(self._name, self._min, value))
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if self._max is not None and value > self._max:
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raise ValueError('Expected %s to be at most %d, not %d' %
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(self._name, self._max, value))
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return value
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class Collection(Field):
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def __init__(self, type, container=tuple):
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"""
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:class:`Field` for storing collections of a given type.
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:param type: all items stored in the collection must be of this type
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:param container: the type to store the items in
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"""
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super(Collection, self).__init__(type=type, default=container())
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def validate(self, value):
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if isinstance(value, basestring):
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raise TypeError('Expected %s to be a collection of %s, not %r'
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% (self._name, self._type.__name__, value))
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for v in value:
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if not isinstance(v, self._type):
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raise TypeError('Expected %s to be a collection of %s, not %r'
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% (self._name, self._type.__name__, value))
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return self._default.__class__(value) or None
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class FieldOwner(type):
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"""Helper to automatically assign field names to descriptors."""
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def __new__(cls, name, bases, attrs):
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for key, value in attrs.items():
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if isinstance(value, Field):
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value._name = key
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return super(FieldOwner, cls).__new__(cls, name, bases, attrs)
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class ImmutableObject(object):
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194
tests/models/test_fields.py
Normal file
194
tests/models/test_fields.py
Normal file
@ -0,0 +1,194 @@
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from __future__ import absolute_import, unicode_literals
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import unittest
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from mopidy.models import * # noqa: F403
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def create_instance(field):
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"""Create an instance of a dummy class for testing fields."""
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class Dummy(object):
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__metaclass__ = FieldOwner
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attr = field
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return Dummy()
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class FieldDescriptorTest(unittest.TestCase):
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def test_raw_field_accesible_through_class(self):
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field = Field()
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instance = create_instance(field)
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self.assertEqual(field, instance.__class__.attr)
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def test_field_knows_its_name(self):
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instance = create_instance(Field())
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self.assertEqual('attr', instance.__class__.attr._name)
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def test_field_has_none_as_default(self):
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instance = create_instance(Field())
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self.assertIsNone(instance.attr)
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def test_field_does_not_store_default_in_dict(self):
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instance = create_instance(Field())
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self.assertNotIn('attr', instance.__dict__)
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def test_field_assigment_and_retrival(self):
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instance = create_instance(Field())
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instance.attr = 1234
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self.assertEqual(1234, instance.attr)
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self.assertEqual(1234, instance.__dict__['attr'])
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def test_field_can_be_reassigned(self):
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instance = create_instance(Field())
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instance.attr = 1234
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instance.attr = 5678
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self.assertEqual(5678, instance.attr)
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def test_field_can_be_deleted(self):
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instance = create_instance(Field())
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instance.attr = 1234
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del instance.attr
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self.assertEqual(None, instance.attr)
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self.assertNotIn('attr', instance.__dict__)
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def test_field_can_be_set_to_none(self):
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instance = create_instance(Field())
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instance.attr = 1234
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instance.attr = None
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self.assertEqual(None, instance.attr)
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self.assertNotIn('attr', instance.__dict__)
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class FieldTest(unittest.TestCase):
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def test_default_handling(self):
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instance = create_instance(Field(default=1234))
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self.assertEqual(1234, instance.attr)
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def test_type_checking(self):
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instance = create_instance(Field(type=set))
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instance.attr = set()
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with self.assertRaises(TypeError):
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instance.attr = 1234
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def test_choices_checking(self):
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instance = create_instance(Field(choices=(1, 2, 3)))
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instance.attr = 1
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with self.assertRaises(TypeError):
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instance.attr = 4
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def test_default_respects_type_check(self):
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with self.assertRaises(TypeError):
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create_instance(Field(type=int, default='123'))
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def test_default_respects_choices_check(self):
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with self.assertRaises(TypeError):
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create_instance(Field(choices=(1, 2, 3), default=5))
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class StringTest(unittest.TestCase):
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def test_default_handling(self):
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instance = create_instance(String(default='abc'))
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self.assertEqual('abc', instance.attr)
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def test_str_allowed(self):
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instance = create_instance(String())
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instance.attr = str('abc')
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self.assertEqual(b'abc', instance.attr)
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def test_unicode_allowed(self):
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instance = create_instance(String())
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instance.attr = unicode('abc')
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self.assertEqual(u'abc', instance.attr)
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def test_other_disallowed(self):
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instance = create_instance(String())
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with self.assertRaises(TypeError):
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instance.attr = 1234
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def test_empty_string(self):
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instance = create_instance(String())
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instance.attr = ''
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self.assertEqual('', instance.attr)
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class IntegerTest(unittest.TestCase):
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def test_default_handling(self):
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instance = create_instance(Integer(default=1234))
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self.assertEqual(1234, instance.attr)
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def test_int_allowed(self):
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instance = create_instance(Integer())
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instance.attr = int(123)
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self.assertEqual(123, instance.attr)
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def test_long_allowed(self):
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instance = create_instance(Integer())
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instance.attr = long(123)
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self.assertEqual(123, instance.attr)
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def test_float_disallowed(self):
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instance = create_instance(Integer())
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with self.assertRaises(TypeError):
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instance.attr = 123.0
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def test_numeric_string_disallowed(self):
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instance = create_instance(Integer())
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with self.assertRaises(TypeError):
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instance.attr = '123'
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def test_other_disallowed(self):
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instance = create_instance(String())
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with self.assertRaises(TypeError):
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instance.attr = tuple()
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def test_min_validation(self):
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instance = create_instance(Integer(min=0))
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instance.attr = 0
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self.assertEqual(0, instance.attr)
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with self.assertRaises(ValueError):
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instance.attr = -1
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def test_max_validation(self):
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instance = create_instance(Integer(max=10))
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instance.attr = 10
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self.assertEqual(10, instance.attr)
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with self.assertRaises(ValueError):
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instance.attr = 11
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class CollectionTest(unittest.TestCase):
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def test_container_instance_is_default(self):
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instance = create_instance(Collection(type=int, container=frozenset))
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self.assertEqual(frozenset(), instance.attr)
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def test_empty_collection(self):
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instance = create_instance(Collection(type=int, container=frozenset))
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instance.attr = []
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self.assertEqual(frozenset(), instance.attr)
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self.assertNotIn('attr', instance.__dict__)
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def test_collection_gets_stored_in_container(self):
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instance = create_instance(Collection(type=int, container=frozenset))
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instance.attr = [1, 2, 3]
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self.assertEqual(frozenset([1, 2, 3]), instance.attr)
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self.assertEqual(frozenset([1, 2, 3]), instance.__dict__['attr'])
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def test_collection_with_wrong_type(self):
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instance = create_instance(Collection(type=int, container=frozenset))
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with self.assertRaises(TypeError):
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instance.attr = [1, '2', 3]
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def test_collection_with_string(self):
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instance = create_instance(Collection(type=int, container=frozenset))
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with self.assertRaises(TypeError):
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instance.attr = '123'
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def test_strings_should_not_be_considered_a_collection(self):
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instance = create_instance(Collection(type=str, container=tuple))
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with self.assertRaises(TypeError):
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instance.attr = b'123'
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