Proper way to remove keys in dictionary with None values in Python

What is the proper way to remove keys from a dictionary with value == None in Python?

Generally, you'll create a new dict constructed from filtering the old one. dictionary comprehensions are great for this sort of thing:

{k: v for k, v in original.items() if v is not None}

If you must update the original dict, you can do it like this ...

filtered = {k: v for k, v in original.items() if v is not None}
original.clear()
original.update(filtered)

This is probably the most "clean" way to remove them in-place that I can think of (it isn't safe to modify a dict while you're iterating over it)

^{Use original.iteritems() on python2.x}

if you need to delete None values recursively, better to use this one:

def delete_none(_dict):
    """Delete None values recursively from all of the dictionaries"""
    for key, value in list(_dict.items()):
        if isinstance(value, dict):
            delete_none(value)
        elif value is None:
            del _dict[key]
        elif isinstance(value, list):
            for v_i in value:
                if isinstance(v_i, dict):
                    delete_none(v_i)

    return _dict

with advice of @dave-cz, there was added functionality to support values in list type.

@mandragor added additional if statement to allow dictionaries which contain simple lists.

Here's also solution if you need to remove all of the None values from dictionaries, lists, tuple, sets:

def delete_none(_dict):
    """Delete None values recursively from all of the dictionaries, tuples, lists, sets"""
    if isinstance(_dict, dict):
        for key, value in list(_dict.items()):
            if isinstance(value, (list, dict, tuple, set)):
                _dict[key] = delete_none(value)
            elif value is None or key is None:
                del _dict[key]

    elif isinstance(_dict, (list, set, tuple)):
        _dict = type(_dict)(delete_none(item) for item in _dict if item is not None)

    return _dict


passed:
a = {
    "a": 12, "b": 34, "c": None,
    "k": {"d": 34, "t": None, "m": [{"k": 23, "t": None},[None, 1, 2, 3],{1, 2, None}], None: 123}
}

returned:
a = {
    "a": 12, "b": 34, 
    "k": {"d": 34, "m": [{"k": 23}, [1, 2, 3], {1, 2}]}
}

For python 2.x:

dict((k, v) for k, v in original.items() if v is not None)