114 lines
2.8 KiB
Python
114 lines
2.8 KiB
Python
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"""Functional utilities."""
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from .abstract import Thenable
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from .promises import promise
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__all__ = [
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'maybe_promise', 'ensure_promise',
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'ppartial', 'preplace', 'ready_promise',
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'starpromise', 'transform', 'wrap',
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]
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def maybe_promise(p):
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"""Return None if p is undefined, otherwise make sure it's a promise."""
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if p:
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if not isinstance(p, Thenable):
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return promise(p)
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return p
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def ensure_promise(p):
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"""Ensure p is a promise.
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If p is not a promise, a new promise is created with p' as callback.
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"""
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if p is None:
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return promise()
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return maybe_promise(p)
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def ppartial(p, *args, **kwargs):
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"""Create/modify promise with partial arguments."""
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p = ensure_promise(p)
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if args:
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p.args = args + p.args
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if kwargs:
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p.kwargs.update(kwargs)
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return p
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def preplace(p, *args, **kwargs):
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"""Replace promise arguments.
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This will force the promise to disregard any arguments
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the promise is fulfilled with, and to be called with the
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provided arguments instead.
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"""
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def _replacer(*_, **__):
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return p(*args, **kwargs)
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return promise(_replacer)
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def ready_promise(callback=None, *args):
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"""Create promise that is already fulfilled."""
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p = ensure_promise(callback)
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p(*args)
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return p
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def starpromise(fun, *args, **kwargs):
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"""Create promise, using star arguments."""
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return promise(fun, args, kwargs)
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def transform(filter_, callback, *filter_args, **filter_kwargs):
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"""Filter final argument to a promise.
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E.g. to coerce callback argument to :class:`int`::
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transform(int, callback)
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or a more complex example extracting something from a dict
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and coercing the value to :class:`float`:
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.. code-block:: python
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def filter_key_value(key, filter_, mapping):
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return filter_(mapping[key])
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def get_page_expires(self, url, callback=None):
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return self.request(
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'GET', url,
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callback=transform(get_key, callback, 'PageExpireValue', int),
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)
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"""
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callback = ensure_promise(callback)
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P = promise(_transback, (filter_, callback, filter_args, filter_kwargs))
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P.then(promise(), callback.throw)
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return P
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def _transback(filter_, callback, args, kwargs, ret):
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try:
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ret = filter_(*args + (ret,), **kwargs)
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except Exception:
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callback.throw()
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else:
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return callback(ret)
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def wrap(p):
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"""Wrap promise.
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This wraps the promise such that if the promise is called with a promise as
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argument, we attach ourselves to that promise instead.
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"""
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def on_call(*args, **kwargs):
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if len(args) == 1 and isinstance(args[0], promise):
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return args[0].then(p)
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else:
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return p(*args, **kwargs)
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return on_call
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