> dict1={1: 4, 3: 5}... and 2 millions element
> dict2={3: 3, 8: 6}... and 3 millions element
>
> I want to combine dict1 and dict2 and i don't want to use FOR because
> i need to performance.

If you combine your dict1 and dict2 to become result_dict, what
should the result of result_dict[3] be? 3 or 5?

It sounds like the .update() method on a dict.

You can do something like

dict2.update(dict1)

or

disc1.update(dict2)

depending on your answer to the above question about what
result_dict[3] should be.

If you need to preserve dict1 and dict2, rather than update one
of them, you can make a copy first:

result_dict = dict(dict1)
result_dict.update(dict2)

this will produce result_dict[3] = 3 whereas if you want it to
return 5, swap the order of dict1 and dict.

-tkc