Formatting multiple lines in Python with method calls

Question

What's the accepted style in Python to format multiple lines of code that are method calls?

my_obj.call(x,y).multiple(*args).methods([1,2,3])

With implicit line breaks after brackets/parentheses it would look like this:

my_obj.call(
  x, y).multiple(
  *args).methods(
  [1,2,3])

Which is a bit ugly and doesn't really fit with typical Python style.

1. Is it acceptable to format multiple method calls with the back slash \?

   my_obj.call(x, y) \
     .multiple(*args) \
     .methods([1,2,3])
   

2. If it is acceptable, is it then also acceptable to use two spaces in the line after for the method call or should there be no indentation?

Leiker

Just my opinion, but I think using backslashes is cleanest, and you should definitely indent the following lines, rather with more than two spaces (again, just my opinion, but I'd probably use two "block"-widths or align the .) – Shelley

Answer 1

I will format it like this:

my_obj.call(
    x, y
).multiple(
    *args
).methods(
    [1, 2, 3]
)

Or use \:

my_obj.call(x, y) \
    .multiple(*args) \
    .methods([1, 2, 3])

The indention should be the same as block indention which is usually 4 spaces.

Altigraph

Can you back this up with a reference, or reasons why this should be preferred? PEP8 seems only to be about long parameter lists, not about method chaining. Not saying that it's wrong, but it seems to be just an opinion... – Shelley

Um... It is the default action in Pycharm. It isn't a rule, but as Pycharm is widely used, it is long-tested. – Altigraph

Answer 2

An alternative to trailing \ is to use parenthesis:

(my_obj.call(x, y)
  .multiple(*args)
  .methods([1,2,3]))

Commissioner

interesting solution! – Leiker

Answer 3

The pep8 way would be

temp_obj = my_obj.call(x,y)
temp_obj = temp_obj.multiple(*args)
temp_obj.methods([1,2,3])

Or if the first line fits in one line i.e < 79 characters.

temp_obj = my_obj.call(x,y).multiple(*args)
temp_obj.methods([1,2,3])

Psi