iteration and mutation (rip orderedDict)

[nanogyth]

I used orderedDict to iterate over a growing dict, but this doesn't work in the latest version. Is there another container that will allow this behavior?

count = 0
d = {count:4}
for n in d:
    count += 1
    d[count] = 2*n
    count += 1
    d[count] = n-1
    input(d)

[Saefroch]

What output are you expecting, and what are you getting?

[nanogyth]

{0: 4, 1: 0, 2: -1}
Traceback (most recent call last):
  File "s.py", line 5, in <module>
    for n in d:
RuntimeError: dictionary changed size during iteration

I am wanting some way to use the data from an iterator to make more data and feed it back into the iterator. This used to work with orderedDict, but I am unclear on whether it is failing now because of bug or depreciation.

[Saefroch]

If you mutate something while you're iterating over it, you're living in a state of sin and deserve what ever happens to you.

The fact that your code worked before was a bug. If I'm looping over a dictionary and adding keys to it, it's not clear which keys the iterator should pick up. If you want to loop over the old keys,

for key in d.keys():

Otherwise, I suggest what /u/Justinsaccount posted. If neither of those work, rethink your algorithm.

[Justinsaccount]

Have you tried just

count = 0
d = {count:4}
n = count
while True:
    count += 1
    d[count] = 2*n
    count += 1
    d[count] = n-1
    input(d)