Case insensitive dictionary

Just for the record. I found an awesome impementation on Requests:

https://github.com/kennethreitz/requests/blob/v1.2.3/requests/structures.py#L37

If I understand you correctly and you want a way to key dictionaries in a non case-sensitive fashion, one way would be to subclass dict and overload the setter / getter:

class CaseInsensitiveDict(dict):
    def __setitem__(self, key, value):
        super(CaseInsensitiveDict, self).__setitem__(key.lower(), value)

    def __getitem__(self, key):
        return super(CaseInsensitiveDict, self).__getitem__(key.lower())

The currently accepted answer wouldn't work for lots of cases, so it cannot be used as a drop-in dict replacement. Some tricky points in getting a proper dict replacement:

• overloading all of the methods that involve keys
• properly handling non-string keys
• properly handling the constructor of the class

The following should work much better:

class CaseInsensitiveDict(dict):
    @classmethod
    def _k(cls, key):
        return key.lower() if isinstance(key, basestring) else key

    def __init__(self, *args, **kwargs):
        super(CaseInsensitiveDict, self).__init__(*args, **kwargs)
        self._convert_keys()
    def __getitem__(self, key):
        return super(CaseInsensitiveDict, self).__getitem__(self.__class__._k(key))
    def __setitem__(self, key, value):
        super(CaseInsensitiveDict, self).__setitem__(self.__class__._k(key), value)
    def __delitem__(self, key):
        return super(CaseInsensitiveDict, self).__delitem__(self.__class__._k(key))
    def __contains__(self, key):
        return super(CaseInsensitiveDict, self).__contains__(self.__class__._k(key))
    def has_key(self, key):
        return super(CaseInsensitiveDict, self).has_key(self.__class__._k(key))
    def pop(self, key, *args, **kwargs):
        return super(CaseInsensitiveDict, self).pop(self.__class__._k(key), *args, **kwargs)
    def get(self, key, *args, **kwargs):
        return super(CaseInsensitiveDict, self).get(self.__class__._k(key), *args, **kwargs)
    def setdefault(self, key, *args, **kwargs):
        return super(CaseInsensitiveDict, self).setdefault(self.__class__._k(key), *args, **kwargs)
    def update(self, E={}, **F):
        super(CaseInsensitiveDict, self).update(self.__class__(E))
        super(CaseInsensitiveDict, self).update(self.__class__(**F))
    def _convert_keys(self):
        for k in list(self.keys()):
            v = super(CaseInsensitiveDict, self).pop(k)
            self.__setitem__(k, v)

In my particular instance, I needed a case insensitive lookup, however, I did not want to modify the original case of the key. For example:

>>> d = {}
>>> d['MyConfig'] = 'value'
>>> d['myconfig'] = 'new_value'
>>> d
{'MyConfig': 'new_value'}

You can see that the dictionary still has the original key, however it is accessible case-insensitively. Here's a simple solution:

class CaseInsensitiveKey(object):
    def __init__(self, key):
        self.key = key
    def __hash__(self):
        return hash(self.key.lower())
    def __eq__(self, other):
        return self.key.lower() == other.key.lower()
    def __str__(self):
        return self.key

The __hash__ and __eq__ overrides are required for both getting and setting entries in the dictionary. This is creating keys that hash to the same position in the dictionary if they are case-insensitively equal.

Now either create a custom dictionary that initializes a CaseInsensitiveKey using the provided key:

class CaseInsensitiveDict(dict):
    def __setitem__(self, key, value):
        key = CaseInsensitiveKey(key)
        super(CaseInsensitiveDict, self).__setitem__(key, value)
    def __getitem__(self, key):
        key = CaseInsensitiveKey(key)
        return super(CaseInsensitiveDict, self).__getitem__(key)

or simply make sure to always pass an instance of CaseInsensitiveKey as the key when using the dictionary.