[Python-Dev] RFC: PEP 509: Add a private version to dict

[Random832]

On Fri, Apr 15, 2016, at 16:41, Victor Stinner wrote:
> If the dictionary values are modified during the loop, the dict
> version is increased. But it's allowed to modify values when you
> iterate on *keys*.

Why is iterating over items different from iterating over keys?

in other words, why do I have to write:

for k in dict:
    v = dict[k]
    ...do some stuff...
    dict[k] = something

rather than

for k, v in dict.items():
    ...do some stuff...
    dict[k] = something


It's not clear why the latter is something you want to prevent.