How to make dictionary read-only?

Use collections.Mapping e.g.

import collections

class DictWrapper(collections.Mapping):

    def __init__(self, data):
        self._data = data

    def __getitem__(self, key): 
        return self._data[key]

    def __len__(self):
        return len(self._data)

    def __iter__(self):
        return iter(self._data)