What is the best way to add entries from 1 dictionary to another?

[bowlofred]

Update is expecting a sequence, each element of which is a mapping (or a sequence of length 2). So you can't feed it a bare tuple, but you can feed it a list of tuples or a dict created from the tuple.

d = {}
item = ('a', 1)

d.update(item)   # won't work
d.update([item]) # okay
d.update({item}) # also okay

That suggests that since it has to take a sequence anyway, you could create one by slicing your original dict rather than using a for loop.

from itertools import islice

groupA = dict(islice(rev_sorted_dataDict.items(), 0, 38) # or....
groupB = {}
groupB.update(islice(rev_sorted_dataDict.items(), 38, 75)