Two-Dimensional Expression Layout

[Michael Selik]

On Fri, Aug 19, 2016 at 5:01 AM Lawrence D’Oliveiro <lawrencedo99 at gmail.com>
wrote:

> It is handy to be able to keep complex expressions together sometimes,
> when breaking them up would simply obscure their structure. To avoid lines
> getting long, why not take advantage of the two available screen/page
> dimensions to make their structure clearer? As a bonus, spacing out
> parentheses makes them look less of a clutter.
>
>

> Examples from <
> https://github.com/ldo/qahirah_examples/blob/master/operators>:
>
> A function call with complex arguments (specifying arguments by keywords
> is highly recommended here):
>
>     rect_1_pattern = \
>         qah.Pattern.create_linear \
>           (
>             p0 = (0, 0),
>             p1 = (major_dim, 0),
>             colour_stops =
>                 (
>                     (0, rect_1_colour),
>                     (1, complement(rect_1_colour)),
>                 )
>           )
>

I'd rather have intermediate variables and avoid the non-semantic
indentation.

    p0 = (0, 0)
    p1 = (major_dim, 0)
    colour_stops = (0, rect_1_colour), (1, complement(rect_1_colour))
    rect_1_pattern = qah.Pattern.create_linear(p0, p1, colour_stops)



Computing a variable value (using redundant parentheses to avoid
> backslash-continuations):
>
>     dest_rect = \
>         (
>             draw_bounds
>         +
>             Vector(col, row) * draw_bounds.dimensions
>         +
>             Vector(0, top_extra)
>         )
>

I'd rather have one long line for this case, even if it's "too long" by PEP
8 standards. If it's too long to think about, I'd break the task into
parts, each with a well-considered variable name.

    substep = a + b
    final = substep + c



>From <https://github.com/ldo/python_pixman/blob/master/pixman.py>, a
> complex condition (with redundant parentheses again):
>
>     if (
>             not isinstance(src, Image)
>         or
>             mask != None and not isinstance(mask, Image)
>         or
>             not isinstance(dest, Image)
>     ) :
>         raise TypeError("image args must be Image objects")
>     #end if
>

No need for the separate calls to isinstance, nor the check for None.

    if any(not isinstance(obj, Image) for obj in [src, mask, dest]):
        ...


If you prefer maps to comprehensions:

    is_image = lambda obj: isinstance(obj, Image)
    if any(map(is_image, [src, mask, dest])):
        ...