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from __future__ import absolute_import
import sys
class promise(object):
if not hasattr(sys, 'pypy_version_info'):
__slots__ = tuple(
'fun args kwargs value ready failed on_success on_error'.split()
)
def __init__(self, fun, args=(), kwargs=(),
on_success=None, on_error=None):
self.fun = fun
self.args = args
self.kwargs = kwargs
self.ready = False
self.failed = False
self.on_success = on_success
self.on_error = on_error
self.value = None
def __repr__(self):
return '<$: {0.fun.__name__}(*{0.args!r}, **{0.kwargs!r})'.format(
self,
)
def __call__(self, *args, **kwargs):
try:
self.value = self.fun(
*self.args + args if self.args else args,
**dict(self.kwargs, **kwargs) if self.kwargs else kwargs
)
except Exception as exc:
self.set_error_state(exc)
else:
if self.on_success:
self.on_success(self.value)
finally:
self.ready = True
def then(self, callback=None, on_error=None):
self.on_success = callback
self.on_error = on_error
return callback
def set_error_state(self, exc):
self.failed = True
if self.on_error is None:
raise
self.on_error(exc)
def throw(self, exc):
try:
raise exc
except exc.__class__ as with_cause:
self.set_error_state(with_cause)
def noop():
return promise(lambda *a, **k: None)
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