| # Copyright 2019 Google LLC |
| # |
| # Licensed under the Apache License, Version 2.0 (the "License"); |
| # you may not use this file except in compliance with the License. |
| # You may obtain a copy of the License at |
| # |
| # https://www.apache.org/licenses/LICENSE-2.0 |
| # |
| # Unless required by applicable law or agreed to in writing, software |
| # distributed under the License is distributed on an "AS IS" BASIS, |
| # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| # See the License for the specific language governing permissions and |
| # limitations under the License. |
| |
| """Provides a simple memoizing decorator.""" |
| |
| |
| def memoize(f): |
| """Memoizes f. |
| |
| The @memoize decorator returns a function which caches the results of f, and |
| returns directly from the cache instead of calling f when it is called again |
| with the same arguments. |
| |
| Memoization has some caveats: |
| |
| Most importantly, the decorated function will not be called every time the |
| function is called. If the memoized function `f` performs I/O or relies on |
| or changes global state, it may not work correctly when memoized. |
| |
| This memoizer only works for functions taking positional arguments. It does |
| not handle keywork arguments. |
| |
| This memoizer only works for hashable arguments -- tuples, ints, etc. It does |
| not work on most iterables. |
| |
| This memoizer returns a function whose __name__ and argument list may differ |
| from the memoized function under reflection. |
| |
| This memoizer never evicts anything from its cache, so its memory usage can |
| grow indefinitely. |
| |
| Depending on the workload and speed of `f`, the memoized `f` can be slower |
| than unadorned `f`; it is important to use profiling before and after |
| memoization. |
| |
| Usage: |
| @memoize |
| def function(arg, arg2, arg3): |
| ... |
| |
| Arguments: |
| f: The function to memoize. |
| |
| Returns: |
| A function which acts like f, but faster when called repeatedly with the |
| same arguments. |
| """ |
| cache = {} |
| |
| def _memoized(*args): |
| assert all(arg.__hash__ for arg in args), ( |
| "Arguments to memoized function {} must be hashable.".format( |
| f.__name__)) |
| if args not in cache: |
| cache[args] = f(*args) |
| return cache[args] |
| |
| return _memoized |