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@leafsummer
Last active September 19, 2021 21:48
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a proxy class example
def _default_cls_attr(name, type_, cls_value):
# Proxy uses properties to forward the standard
# class attributes __module__, __name__ and __doc__ to the real
# object, but these needs to be a string when accessed from
# the Proxy class directly. This is a hack to make that work.
# -- See Issue #1087.
def __new__(cls, getter):
instance = type_.__new__(cls, cls_value)
instance.__getter = getter
return instance
def __get__(self, obj, cls=None):
return self.__getter(obj) if obj is not None else self
return type(name, (type_, ), {
'__new__': __new__, '__get__': __get__,
})
class Proxy(object):
"""Proxy to another object."""
# Code stolen from werkzeug.local.Proxy.
__slots__ = ('__local', '__args', '__kwargs', '__dict__')
def __init__(self, local,
args=None, kwargs=None, name=None, __doc__=None):
object.__setattr__(self, '_Proxy__local', local)
object.__setattr__(self, '_Proxy__args', args or ())
object.__setattr__(self, '_Proxy__kwargs', kwargs or {})
if name is not None:
object.__setattr__(self, '__custom_name__', name)
if __doc__ is not None:
object.__setattr__(self, '__doc__', __doc__)
@_default_cls_attr('name', str, __name__)
def __name__(self):
try:
return self.__custom_name__
except AttributeError:
return self._get_current_object().__name__
@_default_cls_attr('module', str, __module__)
def __module__(self):
return self._get_current_object().__module__
@_default_cls_attr('doc', str, __doc__)
def __doc__(self):
return self._get_current_object().__doc__
def _get_class(self):
return self._get_current_object().__class__
@property
def __class__(self):
return self._get_class()
def _get_current_object(self):
"""Return the current object. This is useful if you want the real
object behind the proxy at a time for performance reasons or because
you want to pass the object into a different context.
"""
loc = object.__getattribute__(self, '_Proxy__local')
if not hasattr(loc, '__release_local__'):
return loc(*self.__args, **self.__kwargs)
try:
return getattr(loc, self.__name__)
except AttributeError:
raise RuntimeError('no object bound to {0.__name__}'.format(self))
@property
def __dict__(self):
try:
return self._get_current_object().__dict__
except RuntimeError: # pragma: no cover
raise AttributeError('__dict__')
def __repr__(self):
try:
obj = self._get_current_object()
except RuntimeError: # pragma: no cover
return '<{0} unbound>'.format(self.__class__.__name__)
return repr(obj)
def __bool__(self):
try:
return bool(self._get_current_object())
except RuntimeError: # pragma: no cover
return False
__nonzero__ = __bool__ # Py2
def __unicode__(self):
try:
return string(self._get_current_object())
except RuntimeError: # pragma: no cover
return repr(self)
def __dir__(self):
try:
return dir(self._get_current_object())
except RuntimeError: # pragma: no cover
return []
def __getattr__(self, name):
if name == '__members__':
return dir(self._get_current_object())
return getattr(self._get_current_object(), name)
def __setitem__(self, key, value):
self._get_current_object()[key] = value
def __delitem__(self, key):
del self._get_current_object()[key]
def __setslice__(self, i, j, seq):
self._get_current_object()[i:j] = seq
def __delslice__(self, i, j):
del self._get_current_object()[i:j]
__setattr__ = lambda x, n, v: setattr(x._get_current_object(), n, v)
__delattr__ = lambda x, n: delattr(x._get_current_object(), n)
__str__ = lambda x: str(x._get_current_object())
__lt__ = lambda x, o: x._get_current_object() < o
__le__ = lambda x, o: x._get_current_object() <= o
__eq__ = lambda x, o: x._get_current_object() == o
__ne__ = lambda x, o: x._get_current_object() != o
__gt__ = lambda x, o: x._get_current_object() > o
__ge__ = lambda x, o: x._get_current_object() >= o
__hash__ = lambda x: hash(x._get_current_object())
__call__ = lambda x, *a, **kw: x._get_current_object()(*a, **kw)
__len__ = lambda x: len(x._get_current_object())
__getitem__ = lambda x, i: x._get_current_object()[i]
__iter__ = lambda x: iter(x._get_current_object())
__contains__ = lambda x, i: i in x._get_current_object()
__getslice__ = lambda x, i, j: x._get_current_object()[i:j]
__add__ = lambda x, o: x._get_current_object() + o
__sub__ = lambda x, o: x._get_current_object() - o
__mul__ = lambda x, o: x._get_current_object() * o
__floordiv__ = lambda x, o: x._get_current_object() // o
__mod__ = lambda x, o: x._get_current_object() % o
__divmod__ = lambda x, o: x._get_current_object().__divmod__(o)
__pow__ = lambda x, o: x._get_current_object() ** o
__lshift__ = lambda x, o: x._get_current_object() << o
__rshift__ = lambda x, o: x._get_current_object() >> o
__and__ = lambda x, o: x._get_current_object() & o
__xor__ = lambda x, o: x._get_current_object() ^ o
__or__ = lambda x, o: x._get_current_object() | o
__div__ = lambda x, o: x._get_current_object().__div__(o)
__truediv__ = lambda x, o: x._get_current_object().__truediv__(o)
__neg__ = lambda x: -(x._get_current_object())
__pos__ = lambda x: +(x._get_current_object())
__abs__ = lambda x: abs(x._get_current_object())
__invert__ = lambda x: ~(x._get_current_object())
__complex__ = lambda x: complex(x._get_current_object())
__int__ = lambda x: int(x._get_current_object())
__float__ = lambda x: float(x._get_current_object())
__oct__ = lambda x: oct(x._get_current_object())
__hex__ = lambda x: hex(x._get_current_object())
__index__ = lambda x: x._get_current_object().__index__()
__coerce__ = lambda x, o: x._get_current_object().__coerce__(o)
__enter__ = lambda x: x._get_current_object().__enter__()
__exit__ = lambda x, *a, **kw: x._get_current_object().__exit__(*a, **kw)
__reduce__ = lambda x: x._get_current_object().__reduce__()
if not PY3:
__cmp__ = lambda x, o: cmp(x._get_current_object(), o) # noqa
__long__ = lambda x: long(x._get_current_object()) # noqa
class PromiseProxy(Proxy):
"""This is a proxy to an object that has not yet been evaulated.
:class:`Proxy` will evaluate the object each time, while the
promise will only evaluate it once.
"""
__slots__ = ('__pending__', )
def _get_current_object(self):
try:
return object.__getattribute__(self, '__thing')
except AttributeError:
return self.__evaluate__()
def __then__(self, fun, *args, **kwargs):
if self.__evaluated__():
return fun(*args, **kwargs)
from collections import deque
try:
pending = object.__getattribute__(self, '__pending__')
except AttributeError:
pending = None
if pending is None:
pending = deque()
object.__setattr__(self, '__pending__', pending)
pending.append((fun, args, kwargs))
def __evaluated__(self):
try:
object.__getattribute__(self, '__thing')
except AttributeError:
return False
return True
def __maybe_evaluate__(self):
return self._get_current_object()
def __evaluate__(self,
_clean=('_Proxy__local',
'_Proxy__args',
'_Proxy__kwargs')):
try:
thing = Proxy._get_current_object(self)
except:
raise
else:
object.__setattr__(self, '__thing', thing)
for attr in _clean:
try:
object.__delattr__(self, attr)
except AttributeError: # pragma: no cover
# May mask errors so ignore
pass
try:
pending = object.__getattribute__(self, '__pending__')
except AttributeError:
pass
else:
try:
while pending:
fun, args, kwargs = pending.popleft()
fun(*args, **kwargs)
finally:
try:
object.__delattr__(self, '__pending__')
except AttributeError:
pass
return thing
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