updating dictionaries from/to dictionaries

[John Machin]

On Aug 11, 6:24 pm, "Calvin Spealman" <ironfro... at gmail.com> wrote:
> for k in foo:
>   foo[k] += bar.get(k, 0)

An alternative:

for k in bar:
   foo[k] += bar[k]

The OP asserts that foo keys are a superset of bar keys. If that
assertion is not true (i.e. there are keys in bar that are not in foo,
your code will silently ignore them whereas mine will cause an
exception to be raised (better behaviour IMHO). If the assertion is
true, mine runs faster (even when len(foo) == len(bar).