[Python-Dev] Add a frozendict builtin type (original) (raw)

Yury Selivanov yselivanov.ml at gmail.com
Fri Mar 2 03:13:44 CET 2012

On 2012-03-01, at 7:50 PM, Guido van Rossum wrote:

I think you should provide stronger arguments in each case why the data needs to be truly immutable or read-only, rather than just using _a convention or an "advisory" API (like private can be circumvented but clearly indicates intent to the reader).

Here's one more argument to support frozendicts.

For last several months I've been thinking about prohibiting coroutines (generators + greenlets in our framework) to modify the global state. If there is a guarantee that all coroutines of the whole application, modules and framework are 100% safe from that, it's possible to do some interesting stuff. For instance, dynamically balance jobs across all application processes:

@coroutine def on_generate_report(context): data = yield fetch_financial_data(context) ...

In the above example, 'fetch_financial_data' may be executed in the different process, or even on the different server, if the coroutines' scheduler of current process decides so (based on its load, or a low priority of the coroutine being scheduled).

With built-in frozendict it will be easier to secure modules or functions' globals that way, allowing to play with features closer to the ones Erlang and other concurrent languages provide.

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