fix(rust,python): Improve printing controls of DataFrame and Series

[slonik-az]

fixes #5046

(1) Let polars.Config.set_tbl_rows to control maximum number of
elements when printing Series (in general any Series => str conversion).
Works the same way as when printing DataFrame.

(2) Calling polars.Config.set_tbl_rows or polars.Config.set_tbl_cols with
any negative integer (-1 is recommended) will cause all the rows
(DataFrame and Series) or all the columns (DataFrame) be printed.

[alexander-beedie]

Nice! Do you think you could tweak the "all rows" value to -1, rather than 0? If I went into a shop and asked for zero apples, I'd be quite surprised if they then gave me all of the apples they had 😄

(On a more realistic note, I can imagine that there may be some --admittedly odd!-- edge-cases where you might actually want to return tables with no rows; overriding zero to mean "all" leaves no way to do so).

[slonik-az]

Nice! Do you think you could tweak the "all rows" value to -1, rather than 0?

Fair enough. For the sake of consistency I will make setting rows (cols) to any negative number (-1,-2,etc) to print all the rows (cols) in a DataFrame or Series.

[slonik-az]

(On a more realistic note, I can imagine that there may be some --admittedly odd!-- edge-cases where you might actually want to return tables with no rows; overriding zero to mean "all" leaves no way to do so).

Actually, in the current polars (as of py-0.14.15) when you set_tbl_rows(0) the actual value used for max rows will be 2, making it impossible to force print zero number of rows. In my PR I keep this existing behavior unchanged.

polars/polars/polars-core/src/fmt.rs

Lines 344 to 348 in 1968f3f

	if max_n_rows < 2 {
	2
	} else {
	max_n_rows
	}

[slonik-az]

Just updated the PR with the requested changes. While at that I squashed all the commits into one and rebased it onto the latest master.

[ritchie46]

Al right. Thanks!

[slonik-az]

@ritchie46: Thanks for promptly merging it in!

[alexander-beedie]

Actually, in the current polars (as of py-0.14.15) when you set_tbl_rows(0) the actual value used for max rows will be 2, making it impossible to force print zero number of rows. In my PR I keep this existing behavior unchanged.

polars/polars/polars-core/src/fmt.rs

Lines 344 to 348 in 1968f3f

	if max_n_rows < 2 {
	2
	} else {
	max_n_rows
	}

Very peculiar :)
Think I might take a look at this separately later to see why; thanks!