85 lines
2.7 KiB
Python
85 lines
2.7 KiB
Python
import contextlib
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import functools
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class BatchController(object):
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''' Batches are sets of operations where certain queries for users may be
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repeated, but are also unlikely change within the boundaries of the batch.
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Batches are keyed per-user. You can mark the edge of the batch with the
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``batch`` context manager. If you nest calls to ``batch``, only the
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outermost call will have the effect of ending the batch.
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Batches store results for functions wrapped with ``memoise``. These results
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for the user are flushed at the end of the batch.
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If a return for a memoised function has a callable attribute called
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``end_batch``, that attribute will be called at the end of the batch.
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'''
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_user_caches = {}
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@classmethod
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@contextlib.contextmanager
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def batch(cls, user):
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''' Marks the entry point for a batch for the given user. '''
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pass
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# TODO: store nesting count *inside* the cache object. You know it
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# makes sense.
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@classmethod
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def memoise(cls, func):
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''' Decorator that stores the result of the stored function in the
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user's results cache until the batch completes.
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Arguments:
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func (callable(user, *a, **k)): The function whose results we want
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to store. ``user`` must be the first argument; this is used as
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the cache key.
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Returns:
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callable(user, *a, **k): The memosing version of ``func``.
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'''
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@functools.wraps(func)
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def f(user, *a, **k):
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cache = cls.get_cache(user)
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if func not in cache:
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cache[func] = func(user, *a, **k)
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return cache[func]
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return f
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@classmethod
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def get_cache(cls, user):
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if user not in cls._user_caches:
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return {} # Return blank cache here, we'll just discard :)
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return cls._user_caches[user]
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'''
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TODO: memoise CartController.for_user
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TODO: memoise user_remainders (Product, Category)
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TODO: memoise _filtered_flags
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TODO: memoise FlagCounter.count() (doesn't take user, but it'll do for now)
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TODO: memoise _filtered_discounts
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Tests:
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- Correct nesting behaviour
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- do we get different cache objects every time we get a cache in non-batched
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contexts?
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- do we get the same cache object for nested caches?
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- do we get different cache objects when we back out of a batch and enter a
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new one
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- are cache clears independent for different users?
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- ``end_batch`` behaviour for CartController (use for_user *A LOT*)
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- discounts not calculated until outermost batch point exits.
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- Revision number shouldn't change until outermost batch point exits.
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- Make sure memoisation ONLY happens when we're in a batch.
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'''
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