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


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.

Asked By: Ryan C. Thompson



From my experience with tutorials, and other things number 2 always seems preferred, but it’s a personal preference choice more than anything else.

Answered By: Jake

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 = (
Answered By: FogleBird

Since your keys are strings and since we are talking about readability, I prefer :

mydict = dict(
    key1 = 1,
    key2 = 2,
    key3 = 3
Answered By: dugres

Generally, you would not include the comma after the final entry, but Python will correct that for you.

Answered By: Joe

First of all, like Steven Rumbalski said, “PEP8 doesn’t address this question”, so it is a matter of personal preference.

I would use a similar but not identical format as your format 3. Here is mine, and why.

my_dictionary = { # Don't think dict(...) notation has more readability
    "key1": 1, # Indent by one press of TAB (i.e. 4 spaces)
    "key2": 2, # Same indentation scale as above
    "key3": 3, # Keep this final comma, so that future addition won't show up as 2-lines change in code diff
    } # My favorite: SAME indentation AS ABOVE, to emphasize this bracket is still part of the above code block!
the_next_line_of_code() # Otherwise the previous line would look like the begin of this part of code

bad_example = {
               "foo": "bar", # Don't do this. Unnecessary indentation wastes screen space
               "hello": "world" # Don't do this. Omitting the comma is not good.
} # You see? This line visually "joins" the next line when in a glance

    foo='hello world',  # So I put one parameter per line
    bar=123,  # And yeah, this extra comma here is harmless too;
              # I bet not many people knew/tried this.
              # Oh did I just show you how to write
              # multiple-line inline comment here?
              # Basically, same indentation forms a natural paragraph.
    ) # Indentation here. Same idea as the long dict case.

# By the way, now you see how I prefer inline comment to document the very line.
# I think this inline style is more compact.
# Otherwise you will need extra blank line to split the comment and its code from others.


# hi this function is blah blah

Answered By: RayLuo

Usually, if you have big python objects it’s quite hard to format them. I personally prefer using some tools for that.

Here is python-beautifier – www.cleancss.com/python-beautify that instantly turns your data into customizable style.

Answered By: Max
dict(rank = int(lst[0]),
                grade = str(lst[1]),
                videos = float(lst[3].replace(",", " ")),
                subscribers = float(lst[4].replace(",", "")),
                views = float(lst[5].replace(",", "")))
Answered By: user11449974

flake8 – a utility for enforcing style consistency in python code, which checks your code syntax and provide instructions to improve it – recommends this format (see https://www.flake8rules.com/rules/E133.html):

mydict = {
    "key1": 1,
    "key2": 2,
    "key3": 3,
Answered By: mouwsy