Which method do you prefer when updating dict?

When updating and adding elements of a dict object, I don't know how to do it neatly.

I understand that the following 2 methods are possible, which of the two do you prefer?

There may be factors that affect individual tastes, but I'm thinking about it because I feel that both are somewhat messy. ㅜ<

a = {original data}

# Method 1
b = {processed data}
a.update(b)

# Method 2
a[processed data] = c
a[processed data] = d
a[processed data] = e
...