atools 0.8.0

Python 3.6+ async/sync memoize and rate decorators

atools

Python 3.6+ decorators including

• memoize - a function decorator for sync and async functions that memoizes results.
• rate - a function decorator for sync and async functions that rate limits calls.

memoize

Decorates a function call and caches return value for given inputs.

If 'size' is provided, memoize will only retain up to 'size' return values.

If 'expire' is provided, memoize will only retain return values for up to 'expire' duration.

If 'gen_key' is provided, memoize will use the function to calculate the memoize hash key.

Examples:

    - Body will run once for unique input 'bar' and result is cached.
        @memoize
        def foo(bar) -> Any: ...

        foo(1)  # Function actually called. Result cached.
        foo(1)  # Function not called. Previously-cached result returned.
        foo(2)  # Function actually called. Result cached.

    - Same as above, but async.
        @memoize
        async def foo(bar) -> Any: ...

        # Concurrent calls from the same event loop are safe. Only one call is generated. The
        other nine calls in this example wait for the result.
        await asyncio.gather(*[foo(1) for _ in range(10)])

    - Classes may be memoized.
        @memoize
        Class Foo:
            def init(self, _): ...

        Foo(1)  # Instance is actually created.
        Foo(1)  # Instance not created. Previously-cached instance returned.
        Foo(2)  # Instance is actually created.

    - Calls to foo(1), foo(bar=1), and foo(1, baz='baz') are equivalent and only cached once
        @memoize
        def foo(bar, baz='baz'): ...

    - Only 2 items are cached. Acts as an LRU.
        @memoize(size=2)
        def foo(bar) -> Any: ...

        foo(1)  # LRU cache order [foo(1)]
        foo(2)  # LRU cache order [foo(1), foo(2)]
        foo(1)  # LRU cache order [foo(2), foo(1)]
        foo(3)  # LRU cache order [foo(1), foo(3)], foo(2) is evicted to keep cache size at 2

   - Items are evicted after 1 minute.
        @memoize(duration=datetime.timedelta(minutes=1))
        def foo(bar) -> Any: ...

        foo(1)  # Function actually called. Result cached.
        foo(1)  # Function not called. Previously-cached result returned.
        sleep(61)
        foo(1)  # Function actually called. Previously-cached result was too old.

    - Memoize can be explicitly reset through the function's 'memoize' attribute
        @memoize
        def foo(bar) -> Any: ...

        foo(1)  # Function actually called. Result cached.
        foo(1)  # Function not called. Previously-cached result returned.
        foo.memoize.reset()
        foo(1)  # Function actually called. Cache was emptied.

    - Current cache size can be accessed through the function's 'memoize' attribute
        @memoize
        def foo(bar) -> Any: ...

        foo(1)
        foo(2)
        len(foo.memoize)  # returns 2

    - Memoization hash keys can be generated from a non-default function:
        @memoize(gen_key=lambda a, b, c: (a, b, c))
        def foo(a, b, c) -> Any: ...

    - If part of the returned key from gen_key is awaitable, it will be awaited.
        async def await_something() -> Hashable: ...

        @memoize(gen_key=lambda bar: (bar, await_something()))
        async def foo(bar) -> Any: ...

    - Properties can be memoized
        Class Foo:
            @property
            @memoize
            def bar(self): -> Any: ...

        a = Foo()
        a.bar  # Function actually called. Result cached.
        a.bar  # Function not called. Previously-cached result returned.

        b = Foo() # Memoize uses 'self' parameter in hash. 'b' does not share returns with 'a'
        b.bar  # Function actually called. Result cached.
        b.bar  # Function not called. Previously-cached result returned.

    - Be careful with eviction on methods.
        Class Foo:
            @memoize(size=1)
            def bar(self, baz): -> Any: ...

        a, b = Foo(), Foo()
        a.bar(1)  # LRU cache order [Foo.bar(a, 1)]
        b.bar(1)  # LRU cache order [Foo.bar(b, 1)], Foo.bar(a, 1) is evicted
        a.bar(1)  # Foo.bar(a, 1) is actually called and cached again.

rate

Function decorator that rate limits the number of calls to function.

'size' must be provided. It specifies the maximum number of calls that may be made concurrently
  and optionally within a given 'duration' time window.

If 'duration' is provided, the maximum number of calls is limited to 'size' calls in any given
  'duration' time window.

Examples:
    - Only 2 concurrent calls allowed.
        @rate(size=2)
        def foo(): ...

    - Only 2 calls allowed per minute.
        @rate(size=2, duration=60)
        def foo(): ...

    - Same as above, but duration specified with a timedelta.
        @rate_window(size=2, duration=datetime.timedelta(minutes=1))
        def foo(): ...

    - Same as above, but async.
        @rate_window(size=2, duration=datetime.timedelta(minutes=1))
        async def foo(): ...