Question

What is this convention of splitting arguments into lines? Is there a PEP that sanctions this? I did not find it in PEP8.

file_like = f(self,
              path,
              mode=mode,
              buffering=buffering,
              encoding=encoding,
              errors=errors,
              newline=newline,
              line_buffering=line_buffering,
              **kwargs)

Answer 1

It's for the (A) Vertical Alignment to be used when (B) Max Line Length will get exceeded, and sometimes even if it won't - for better readability.

These are the first 3 examples on that page illustrating it:

Yes:

# Aligned with opening delimiter.
foo = long_function_name(var_one, var_two,
                         var_three, var_four)

# More indentation included to distinguish this from the rest.
def long_function_name(
        var_one, var_two, var_three,
        var_four):
    print(var_one)

# Hanging indents should add a level.
foo = long_function_name(
    var_one, var_two,
    var_three, var_four)

The one you asked about is a variation of the first example above, with only one arg per line for clarity.

No:

# Arguments on first line forbidden when not using vertical alignment.
foo = long_function_name(var_one, var_two,
    var_three, var_four)

And (C), the arguments with the name given (keyword arguments) is done so that you don't need to lookup what the parameters are in the called function. Typically, every non-obvious parameter which may act like a flag or modifier to the core functionality of the called function should be passed as a keyword argument. Ex:

> read_file('abc.txt', 1024, True)  # yes, you know 'abc.txt' is the filename
> # What are the 1024 and True for?
> # versus...
> read_file('abc.txt', max_lines=1024, output_as_list=True)  # now you know what it does.

PS: The answer by @falsetru isn't wrong. Max line length is the first reason to re-format your code. As for the specific reason to align it that way, that's vertical alignment.

Answer 2

Maximum Line Length: If it was not splitted into multiple lines, the line length would be more than 79 characters.

Python what code convention splitting arguments into lines?

2 个答案: