| # Copyright 2019 The LUCI Authors. All rights reserved. |
| # Use of this source code is governed under the Apache License, Version 2.0 |
| # that can be found in the LICENSE file. |
| |
| """Helpers for writing classes.""" |
| |
| |
| def cached_property(getter): |
| """A very basic @property-style decorator for read-only cached properties. |
| |
| The result of the first successful call to `getter` will be cached on `self` |
| with the key _cached_property_{getter.__name__}. |
| """ |
| key = '_cached_property_%s' % (getter.__name__,) |
| |
| @property |
| def _inner(self): |
| if not hasattr(self, key): |
| # object.__setattr__ is needed to cheat attr.s' freeze. This is the |
| # documented way to work around the lack of fine-grained immutability. |
| object.__setattr__(self, key, getter(self)) |
| return getattr(self, key) |
| |
| return _inner |
