/usr/share/pyshared/epsilon/descriptor.py is in python-epsilon 0.6.0-3.
This file is owned by root:root, with mode 0o644.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 | # -*- test-case-name: epsilon.test.test_descriptor -*-
"""
Provides an 'attribute' class for one-use descriptors.
"""
attribute = None
class _MetaAttribute(type):
def __new__(meta, name, bases, dict):
# for reals, yo.
for kw in ['get', 'set', 'delete']:
if kw in dict:
dict[kw] = staticmethod(dict[kw])
secretClass = type.__new__(meta, name, bases, dict)
if attribute is None:
return secretClass
return secretClass()
class attribute(object):
"""
Convenience class for providing one-shot descriptors, similar to
'property'. For example:
>>> from epsilon.descriptor import attribute
>>> class Dynamo(object):
... class dynamic(attribute):
... def get(self):
... self.dynCount += 1
... return self.dynCount
... def set(self, value):
... self.dynCount += value
... dynCount = 0
...
>>> d = Dynamo()
>>> d.dynamic
1
>>> d.dynamic
2
>>> d.dynamic = 6
>>> d.dynamic
9
>>> d.dynamic
10
>>> del d.dynamic
Traceback (most recent call last):
...
AttributeError: attribute cannot be removed
"""
__metaclass__ = _MetaAttribute
def __get__(self, oself, type):
"""
Private implementation of descriptor interface.
"""
if oself is None:
return self
return self.get(oself)
def __set__(self, oself, value):
"""
Private implementation of descriptor interface.
"""
return self.set(oself, value)
def __delete__(self, oself):
"""
Private implementation of descriptor interface.
"""
return self.delete(oself)
def set(self, value):
"""
Implement this method to provide attribute setting. Default behavior
is that attributes are not settable.
"""
raise AttributeError('read only attribute')
def get(self):
"""
Implement this method to provide attribute retrieval. Default behavior
is that unset attributes do not have any value.
"""
raise AttributeError('attribute has no value')
def delete(self):
"""
Implement this method to provide attribute deletion. Default behavior
is that attributes cannot be deleted.
"""
raise AttributeError('attribute cannot be removed')
def requiredAttribute(requiredAttributeName):
"""
Utility for defining attributes on base classes/mixins which require their
values to be supplied by their derived classes. C{None} is a common, but
almost never suitable default value for these kinds of attributes, as it
may cause operations in the derived class to fail silently in peculiar
ways. If a C{requiredAttribute} is accessed before having its value
changed, a C{AttributeError} will be raised with a helpful error message.
@param requiredAttributeName: The name of the required attribute.
@type requiredAttributeName: C{str}
Example:
>>> from epsilon.descriptor import requiredAttribute
...
>>> class FooTestMixin:
... expectedResult = requiredAttribute('expectedResult')
...
>>> class BrokenFooTestCase(TestCase, FooTestMixin):
... pass
...
>>> brokenFoo = BrokenFooTestCase()
>>> print brokenFoo.expectedResult
Traceback (most recent call last):
...
AttributeError: Required attribute 'expectedResult' has not been
changed from its default value on '<BrokenFooTestCase
instance>'.
...
>>> class WorkingFooTestCase(TestCase, FooTestMixin):
... expectedResult = 7
...
>>> workingFoo = WorkingFooTestCase()
>>> print workingFoo.expectedResult
... 7
>>>
"""
class RequiredAttribute(attribute):
def get(self):
if requiredAttributeName not in self.__dict__:
raise AttributeError(
('Required attribute %r has not been changed'
' from its default value on %r' % (
requiredAttributeName, self)))
return self.__dict__[requiredAttributeName]
def set(self, value):
self.__dict__[requiredAttributeName] = value
return RequiredAttribute
__all__ = ['attribute', 'requiredAttribute']
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