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

Question

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

Answer 1

You can also do this using the del command

   f = {};
   f['win']=None
   f
   => {'win': None}
   del f['win']

Or if you want this in a function format you could do:

def del_none_keys(dict):
    for elem in dict.keys():
        if dict[elem] == None:
           del dict[elem]

Answer 2

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}

Answer 3

You could also take a copy of the dict to avoid iterating the original dict while altering it.

for k, v in dict(d).items():
    if v is None:
        del d[k]

But that might not be a great idea for larger dictionaries.

Answer 4

For python 2.x:

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

Answer 5

Maybe you'll find it useful:

def clear_dict(d):
    if d is None:
        return None
    elif isinstance(d, list):
        return list(filter(lambda x: x is not None, map(clear_dict, d)))
    elif not isinstance(d, dict):
        return d
    else:
        r = dict(
                filter(lambda x: x[1] is not None,
                    map(lambda x: (x[0], clear_dict(x[1])),
                        d.items())))
        if not bool(r):
            return None
        return r

it would:

clear_dict(
    {'a': 'b', 'c': {'d': [{'e': None}, {'f': 'g', 'h': None}]}}
)

->

{'a': 'b', 'c': {'d': [{'f': 'g'}]}}

Answer 6

if you don't want to make a copy

for k,v  in list(foo.items()):
   if v is None:
      del foo[k]