How can I avoid “RuntimeError: dictionary changed size during iteration” error?

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.