在 python 中，如果可能，如何调整黑色格式化程序？

Question

I know that Black is an opinionated formatter, but I love everything it does except one major thing. When I have a function with multiple arguments, instead of displaying it like this:

def example_function(arg_1: str, arg_2: bool, arg_3: int = 0, arg_4: int = 1, arg_5: float = 0.0):
    pass

I'd rather display it as follows for readability

def example_function(
    arg_1: str, 
    arg_2: bool, 
    arg_3: int = 0, 
    arg_4: int = 1, 
    arg_5: float = 0.0
):

Is this achievable with Black or some other formatter? I have this problem several times and it makes me consider not to use Black, either something else or nothing at all. Any ideas or comments?

Answer 1

This is due to the default line length for black being longer than you'd like – 88 characters per line .

To decrease the line length, you can use the --line-length flag as documented here:

https://github.com/psf/black/blob/master/docs/installation_and_usage.md#command-line-options

For example:

$ black --line-length 80 example.py

Black explains the --line-length setting in more detail here:

https://github.com/psf/black/blob/master/docs/the_black_code_style.md#line-length

Line length

You probably noticed the peculiar default line length. Black defaults to 88 characters per line, which happens to be 10% over 80. This number was found to produce significantly shorter files than sticking with 80 (the most popular), or even 79 (used by the standard library). In general, 90-ish seems like the wise choice .

If you're paid by the line of code you write, you can pass --line-length with a lower number. Black will try to respect that. However, sometimes it won't be able to without breaking other rules. In those rare cases, auto-formatted code will exceed your allotted limit.

You can also increase it, but remember that people with sight disabilities find it harder to work with line lengths exceeding 100 characters. It also adversely affects side-by-side diff review on typical screen resolutions. Long lines also make it harder to present code neatly in documentation or talk slides.

Emphasis on the final paragraph.

I'd recommend just keeping the default settings. The beauty of Black is that it chooses for you, and therefor preempts any arguments about which way is "best" .

Answer 2

This is now possible by adding a trailing comma to your last argument.

In your example you would write instead:

def example_function(
    arg_1: str, 
    arg_2: bool, 
    arg_3: int = 0, 
    arg_4: int = 1, 
    arg_5: float = 0.0, # <-- Notice the trailing comma
):

Answer 3

When using the Black playground at https://black.now.sh , I found that your function was reformatted exactly like that when the line length was short enough (in particular, at 78 characters).

It might be nice if there were a special configuration option that controlled the line length specifically for function parameter lines. BUT to seems to me that Black's configuration-free approach means that there is no way to control this with any more tailored option.