python: union keys from multiple dictionary?

Question

I have 5 dictionaries and I want a union of their keys.

alldict =  [dict1, dict2, dict3, dict4, dict5]

I tried

allkey = reduce(         


        

Answer 1

A simple strategy for non-functional neurons (pun intended):

allkey = []

for dictio in alldict:
    for key in dictio:
        allkey.append(key)

allkey = set(allkey)

We can convert this code to a much sorter form using set comprehensions:

allkey = {key for dictio in alldict for key in dictio}

This one-liner is still very readable in comparison with the conventional for loop. The key to convert a nested loop to a list or set comprehension is to write the inner loop (the one that varies faster in the nested loop) as the last index (that is, for key in dictio).