What is the proper way to format a multi-line dict in Python?

Question

In Python, I want to write a multi-line dict in my code. There are a couple of ways one could format it. Here are a few that I could think of:

1. mydict = { "key1": 1,
              "key2": 2,
              "key3": 3, }
   

2. mydict = { "key1": 1,
              "key2": 2,
              "key3": 3,
            }
   

3. mydict = {
       "key1": 1,
       "key2": 2,
       "key3": 3,
   }
   

I know that any of the above is syntactically correct, but I assume that there is one preferred indentation and line-break style for Python dicts. What is it?

Note: This is not an issue of syntax. All of the above are (as far as I know) valid Python statements and are equivalent to each other.

Answer 1

I use #3. Same for long lists, tuples, etc. It doesn't require adding any extra spaces beyond the indentations. As always, be consistent.

mydict = {
    "key1": 1,
    "key2": 2,
    "key3": 3,
}

mylist = [
    (1, 'hello'),
    (2, 'world'),
]

nested = {
    a: [
        (1, 'a'),
        (2, 'b'),
    ],
    b: [
        (3, 'c'),
        (4, 'd'),
    ],
}

Similarly, here's my preferred way of including large strings without introducing any whitespace (like you'd get if you used triple-quoted multi-line strings):

data = (
    "iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAABG"
    "l0RVh0U29mdHdhcmUAQWRvYmUgSW1hZ2VSZWFkeXHJZTwAAAEN"
    "xBRpFYmctaKCfwrBSCrRLuL3iEW6+EEUG8XvIVjYWNgJdhFjIX"
    "rz6pKtPB5e5rmq7tmxk+hqO34e1or0yXTGrj9sXGs1Ib73efh1"
    "AAAABJRU5ErkJggg=="
)