Break very long lines with access to deeply nested dictionaries

Question

I access a deeply nested dictionary and want to break very long lines properly. Let's assume I have this and want to break the line to conform with PEP8. (The actual line is of course longer, this is just an example.)

some_dict['foo']['bar']['baz'] = 1

How would you break the line, assuming the whole

some_dict['foo']['bar']['baz']

does not fit on one line anymore? There are a lot of examples for breaking long lines, but I couldn't find one for this dictionary access based question.

Update: Please note that I want to assign something to that dictionary. The proposed duplicate only talks about getting a value from that kind of dictionary.

Answer 1

Here's the solution I'm most happy with. It boils down to:

some_dict['foo']['bar']['baz'] = 1

is equal to

(some_dict['foo']['bar']['baz']) = 1

which you can break anywhere you want, like so:

(some_dict['foo']
          ['bar']['baz']) = 1

Which should be aligned with Pythons preferred way to break long lines, using Python's implied line continuation inside parentheses.

Answer 2

If you are dealing with deeply nested dictionaries, you should consider another data structure, refactoring with tuple keys, or defining your path via a list.

Here's an example of the last option which helps specifically with PEP8:

from operator import getitem
from functools import reduce

def get_val(dataDict, mapList):
    return reduce(getitem, mapList, dataDict)

d = {'foo': {'bar': {}}}

*path, key = ['foo', 'bar', 'baz']

get_val(d, path)[key] = 1

Note that lists don't need line escapes between elements. This is perfectly fine:

*path, key = ['foo',
              'bar',
              'baz']