Dictionary infinite loop is exiting unexpectedly

In this case, like @benvc wrote, this is not guaranteed to work. But in case you wonder why does it work in C-Python:

The C-Python implementation destroys the dict object after some inserts and copies it to a new space in memory. It does not care about deletions. So when this happens, the loop notices it and breaking with an exception.

Check out this link if you want to read more about this, and many other interesting python internals here.

https://github.com/satwikkansal/wtfpython#-modifying-a-dictionary-while-iterating-over-it

There is no guarantee that you will iterate over all your dict entries if you mutate it in your loop. From the docs:

Iterating views while adding or deleting entries in the dictionary may raise a RuntimeError or fail to iterate over all entries.

You could create an "enumerated" infinite loop similar to your initial attempt using itertools.count(). For example:

from itertools import count

for i in count():
    print(i)
    # don't run this without some mechanism to break the loop, i.e.
    # if i == 10:
    #     break

# OUTPUT
# 0
# 1
# 2
# ...and so on