Exposes the immutable
dictproxy type to all (?) versions of Python.
PEP416 asked for a
frozendict type, but was rejected. The alternative was
to publicly expose
dictproxy, the type used for and immutable object's
__dict__, which wraps an existing dict and provides a read-only interface
to it. The type has existed since 2.2, but it's never had a Python-land
Until now. But only in 3.3+. Which is not all that helpful to some of us.
This module clumsily exposes the same type to previous versions of Python.
from dictproxyhack import dictproxy myproxy = dictproxy(dict(foo="bar")) print(myproxy['foo']) myproxy['baz'] = "quux" # TypeError
Since the proxy holds a reference to the underlying
dict (but doesn't provide
any way to get it back), you can trivially implement
def frozendict(*args, **kwargs): return dictproxy(dict(*args, **kwargs))
Might as well just inline that where you need it, really.
Python. Should work anywhere. Maybe.
On Python 3.3+, you get the real
mappingproxy type, which lives in the
types module as
On CPython 2.5+, you get a fake class that forcibly instantiates
dictproxy objects via
On nearly anything else, you get a regular class that wraps a dict and doesn't implement any mutating parts of the mapping interface. Not a fabulous solution, but good enough, and only applies until your favorite port catches up with 3.3's standard library.
On non-C Python ports that predate 2.6, you get pretty much a
Mapping ABC doesn't even exist. Sorry.
The shim classes also fool
issubclass, so your dirty
typechecking should work equally poorly anywhere.
I've only actually tried this library on CPython 2.6, 2.7, 3.2, 3.3, and PyPy 2.1, but I'm interested in hearing whether it works elsewhere.
dictproxy. Python 3.3+ won't let you, and the shims for other
versions are of extremely dubious use.
dictproxy has been renamed to
mappingproxy in 3.3+, so don't rely on
repr to match across versions or anything. (It seemed apropos to use the
older name for this module.)