How can I avoid "RuntimeError: dictionary changed size during iteration" error?
dictionary, list, loops, python
Solution
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 on Python 3.x, `.keys` returns a view object instead, so it won't fix your error.
Problem
Suppose I have a dictionary of lists: ``` d = {'a': [1], 'b': [1, 2], 'c': [], 'd':[]} ``` Now I want to remove key-value pairs where the values are empty lists. I tried this code: ``` for i in d: if not d[i]: d.pop(i) ``` but this gives an error: ``` RuntimeError: dictionary changed size during iteration ``` I understand that entries can't be added or removed from a dictionary while iterating through it. How can I work around this limitation in order to solve the problem? See Modifying a Python dict while iterating over it for citations that this can cause problems, and why.