removing dictionary entries with no values- Python

Question

If I have a dictionary, and I want to remove the entries in which the value is an empty list [] how would I go about doing that?

I tried:

for x in dict2.keys():
    if dict2[x] == []:
        dict2.keys().remove(x)

but that didn't work.

JBernardo · Accepted Answer · 2011-06-10 14:25:22Z

14

Newer versions of python support dict comprehensions:

dic = {i:j for i,j in dic.items() if j != []}

These are much more readable than filter or for loops

answered Jun 10, 2011 at 14:25

JBernardo

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Comments

user1114 · Accepted Answer · 2011-06-10 14:23:33Z

12

.keys() provides access to the list of keys in the dictionary, but changes to it are not (necessarily) reflected in the dictionary. You need to use del dictionary[key] or dictionary.pop(key) to remove it.

Because of the behaviour in some version of Python, you need to create a of copy of the list of your keys for things to work right. So your code would work if written as:

for x in list(dict2.keys()):
    if dict2[x] == []:
        del dict2[x]

edited Jun 10, 2011 at 14:23

answered Jun 10, 2011 at 14:05

user1114

1

3 Comments

mklauber Over a year ago

Does not work, because you cannot change the size of a dictionary during iteration.

user1114 Over a year ago

Corrected for Python 2.5/2.6/2.7/3.1.

user1114 Over a year ago

In Python 3 it behaves differently, and gets angry if you modify the dict while iterating over .keys(). (Python 2 automatically creates a list, I believe.)

Ravi · Accepted Answer · 2011-06-10 14:05:28Z

3

for x in dict2.keys():
    if dict2[x] == []:
        del dict2[x]

answered Jun 10, 2011 at 14:05

Ravi

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2 Comments

mklauber Over a year ago

Using .keys() creates a new list to iterate, allowing you to delete from the original. Good Work

user1114 Over a year ago

It does not do so in Python 3, and this will raise RuntimeError: dictionary changed size during iteration.

KrzysztofCiba · Accepted Answer · 2012-12-03 21:08:18Z

3

Why not just keep those which are not empty and let the gc to delete leftovers? I mean:

dict2 = dict( [ (k,v) for (k,v) in dict2.items() if v] )

answered Dec 3, 2012 at 21:08

KrzysztofCiba

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Comments

MattH · Accepted Answer · 2011-06-10 14:02:15Z

1

for key in [ k for (k,v) in dict2.items() if not v ]:
  del dict2[key]

answered Jun 10, 2011 at 14:02

MattH

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Roman Bodnarchuk · Accepted Answer · 2011-06-10 14:05:29Z

1

Clean one, but it will create copy of that dict:

dict(filter(lambda x: x[1] != [], d.iteritems()))

answered Jun 10, 2011 at 14:05

Roman Bodnarchuk

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Comments

Artsiom Rudzenka · Accepted Answer · 2011-06-10 14:40:14Z

1

With generator object instead of list:

a = {'1': [], 'f':[1,2,3]}
dict((data for data in a.iteritems() if data[1]))

answered Jun 10, 2011 at 14:40

Artsiom Rudzenka

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Comments

azgrammer · Accepted Answer · 2015-08-21 21:45:44Z

1

def dict_without_empty_values(d):
    return {k:v for k,v in d.iteritems() if v}


# Ex;
dict1 = {
    'Q': 1,
    'P': 0,
    'S': None,
    'R': 0,
    'T': '',
    'W': [],
    'V': {},
    'Y': None,
    'X': None,
}

print dict1
# {'Q': 1, 'P': 0, 'S': None, 'R': 0, 'T': '', 'W': [], 'V': {}, 'Y': None, 'X': None}

print dict_without_empty_values(dict1)
# {'Q': 1}

answered Aug 21, 2015 at 21:45

azgrammer

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1 Comment

user482963 Over a year ago

how can we do this is in python2.6?

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