How to avoid "RuntimeError: dictionary changed size during iteration" error?
This worked for me:
d = {1: 'a', 2: '', 3: 'b', 4: '', 5: '', 6: 'c'}
for key, value in list(d.items()):
if value == '':
del d[key]
print(d)
# {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
.
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.
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.items() if v}
>>> d
{'a': [1], 'b': [1, 2]}
For this in Python 2:
>>> 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]}
You only need to use copy
:
This way you iterate over the original dictionary fields and on the fly can change the desired dict d
.
It works 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]}
(BTW - Generally to iterate over copy of your data structure, instead of using .copy
for dictionaries or slicing [:]
for lists, you can use import copy
-> copy.copy
(for shallow copy which is equivalent to copy
that is supported by dictionaries or slicing [:]
that is supported by lists) or copy.deepcopy
on your data structure.)