Modifying a Python dict while iterating over it

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Alex Martelli weighs in on this here.

It may not be safe to change the container (e.g. dict) while looping over the container.
So del d[f(k)] may not be safe. As you know, the workaround is to use d.copy().items() (to loop over an independent copy of the container) instead of d.iteritems() or d.items() (which use the same underlying container).

It is okay to modify the value at an existing index of the dict, but inserting values at new indices (e.g. d[g(k)]=v) may not work.

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