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import functools
import logging
log = logging.getLogger(__name__)
class Future(object):
error_on_callbacks = False # and errbacks
def __init__(self):
self.is_done = False
self.value = None
self.exception = None
self._callbacks = []
self._errbacks = []
def succeeded(self):
return self.is_done and not bool(self.exception)
def failed(self):
return self.is_done and bool(self.exception)
def retriable(self):
try:
return self.exception.retriable
except AttributeError:
return False
def success(self, value):
assert not self.is_done, 'Future is already complete'
self.value = value
self.is_done = True
if self._callbacks:
self._call_backs('callback', self._callbacks, self.value)
return self
def failure(self, e):
assert not self.is_done, 'Future is already complete'
self.exception = e if type(e) is not type else e()
assert isinstance(self.exception, BaseException), (
'future failed without an exception')
self.is_done = True
self._call_backs('errback', self._errbacks, self.exception)
return self
def add_callback(self, f, *args, **kwargs):
if args or kwargs:
f = functools.partial(f, *args, **kwargs)
if self.is_done and not self.exception:
self._call_backs('callback', [f], self.value)
else:
self._callbacks.append(f)
return self
def add_errback(self, f, *args, **kwargs):
if args or kwargs:
f = functools.partial(f, *args, **kwargs)
if self.is_done and self.exception:
self._call_backs('errback', [f], self.exception)
else:
self._errbacks.append(f)
return self
def add_both(self, f, *args, **kwargs):
self.add_callback(f, *args, **kwargs)
self.add_errback(f, *args, **kwargs)
return self
def chain(self, future):
self.add_callback(future.success)
self.add_errback(future.failure)
return self
def _call_backs(self, back_type, backs, value):
for f in backs:
try:
f(value)
except Exception as e:
log.exception('Error processing %s', back_type)
if self.error_on_callbacks:
raise e
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