How to avoid "RuntimeError: dictionary changed size during iteration" error?
I have checked all of the other questions with the same error yet found no helpful solution =/
I have a dictionary of lists:
d = {'a': [1], 'b': [1, 2], 'c': [], 'd':[]}
in which some of the values are empty. At the end of creating these lists, I want to remove these empty lists before returning my dictionary. Current I am attempting to do this as follows:
for i in d:
if not d[i]:
d.pop(i)
however, this is giving me the runtime error. I am aware that you cannot add/remove elements in a dictionary while iterating through it...what would be a way around this then?
Solution 1:
In Python 3.x and 2.x you can use use list
to force a copy of the keys to be made:
for i in list(d):
In Python 2.x calling keys
made a copy of the keys that you could iterate over while modifying the dict
:
for i in d.keys():
But note that in Python 3.x this second method doesn't help with your error because keys
returns an a view object instead of copynig the keys into a list.
Solution 2:
You only need to use "copy":
On that's way you iterate over the original dictionary fields and on the fly can change the desired dict (d dict). It's work on each python version, so it's more clear.
In [1]: d = {'a': [1], 'b': [1, 2], 'c': [], 'd':[]}
In [2]: for i in d.copy():
...: if not d[i]:
...: d.pop(i)
...:
In [3]: d
Out[3]: {'a': [1], 'b': [1, 2]}
Solution 3:
Just use dictionary comprehension to copy the relevant items into a new dict
>>> d
{'a': [1], 'c': [], 'b': [1, 2], 'd': []}
>>> d = { k : v for k,v in d.iteritems() if v}
>>> d
{'a': [1], 'b': [1, 2]}
For this in Python 3
>>> d
{'a': [1], 'c': [], 'b': [1, 2], 'd': []}
>>> d = { k : v for k,v in d.items() if v}
>>> d
{'a': [1], 'b': [1, 2]}
Solution 4:
This worked for me:
dict = {1: 'a', 2: '', 3: 'b', 4: '', 5: '', 6: 'c'}
for key, value in list(dict.items()):
if (value == ''):
del dict[key]
print(dict)
# dict = {1: 'a', 3: 'b', 6: 'c'}
Casting the dictionary items to list creates a list of its items, so you can iterate over it and avoid the RuntimeError
.