Formatting of pandas expressions suboptimal for readability

[clstaudt]

Arguing with the formatting decisions of black may be besides the point, but I am pretty happy with it with the exception of one type of expressions:

        trend = matching_items.groupby(pandas.Grouper(key="ERDAT", freq=timeframe))[
            "KWMENG"
        ].sum()

This is a typical pandas expression where some method calls are chained and fields of the dataframe are selected. Black seems to treat the field selection as a list and indents it on a new line. I think this is counterintuitive and does not improve readability. Is it intentional or a potential enhancement to treat this differently?

Operating system: macOS
Python version: 3.7.0
Black version: '18.9b0'

[tuchandra]

This seems related to #571 - I'll +1 this as something that seems kind of bizarre.

[swenzel]

black won't reformat this unless your line is > line-length.
In one line, your statement would be 91 chars, the default line-length is 88.
Two solutions for that, either increase line-length or refactor your code so you get multiple shorter lines. For example:

grouper = pandas.Grouper(key="ERDAT", freq=timeframe)
grouped_items = matching_items.groupby(grouper)
trend = grouped_items["KWMENG"].sum()

88 isn't much, I prefer 120. None the less, I'd also do the refactoring. This way you can provide more descriptive code. I'm certain you can find better names for grouper and grouped_items but you see what I mean.

Long lines with lots of in-line code and logic really aren't that great for readability...

[clstaudt]

"One of the hardest things in programming is naming things" - and especially intermediate results in pandas transform chains, that's why you are going to have a hard time convincing pandas power users to adopt the unusual style you propose. I am going to disagree and say that chained method calls can be great for readability if formatted correctly.

Changing line length would be a workaround for this specific example, but I don't believe it solves the underlying issue.

[zsol]

Let's keep the discussion in #571