[Python-Dev] PEP 416: Add a frozendict builtin type

[Victor Stinner]

Le 29/02/2012 19:21, Victor Stinner a écrit :
> Rationale
> =========
>
> (...) Use cases of frozendict: (...)

I updated the PEP to list use cases described in the other related 
mailing list thread.
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Use cases:

  * frozendict lookup can be done at compile time instead of runtime 
because the mapping is read-only. frozendict can be used instead of a 
preprocessor to remove conditional code at compilation, like code 
specific to a debug build.
  * hashable frozendict can be used as a key of a mapping or as a member 
of set. frozendict can be used to implement a cache.
  * frozendict avoids the need of a lock when the frozendict is shared 
by multiple threads or processes, especially hashable frozendict. It 
would also help to prohibe coroutines (generators + greenlets) to modify 
the global state.
  * frozendict helps to implement read-only object proxies for security 
modules. For example, it would be possible to use frozendict type for 
__builtins__ mapping or type.__dict__. This is possible because 
frozendict is compatible with the PyDict C API.
  * frozendict avoids the need of a read-only proxy in some cases. 
frozendict is faster than a proxy because getting an item in a 
frozendict is a fast lookup whereas a proxy requires a function call.
  * use a frozendict as the default value of function argument: avoid 
the problem of mutable default argument.
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Victor