Support Markdown tables without padding

[Synse]

This PR makes it possible to render markdown tables without padding using the existing is_padding argument.

Rendering a table with a header or value that is extremely long results in an excessively padded table. While the resulting table is (potentially) easier for humans to read, it is functionally equivalent¹ once the markdown is rendered.

When using the table somewhere with limited space (e.g., a GitHub issue/PR body) not having the padding allows for a "larger" table (no characters wasted on padding) or more content in addition to the table.

Note

The is_padding argument removes the padding today but the header separator row requires at least one - for proper rendering. With this change you can write a valid markdown table, without padding.

👀 Usage and Examples

Pass is_padding=False to MarkdownTableWriter to render a table without padding. The existing default behavior (table with padding) remains unchanged.

>>> from pytablewriter import MarkdownTableWriter
>>> MarkdownTableWriter(headers=["foo", "bar"], value_matrix=[["one really long string", 123456],["foo", 1381290238121]], is_padding=False).write_table()
|foo|bar|
|---|--:|
|one really long string|123456|
|foo|1381290238121|
>>> MarkdownTableWriter(headers=["foo", "bar"], value_matrix=[["one really long string", 123456],["foo", 1381290238121]]).write_table()
|         foo          |     bar     |
|----------------------|------------:|
|one really long string|       123456|
|foo                   |1381290238121|
>>> 

These two tables are equivalent when rendered:

With padding (current behavior)

|row|    a longer column name    | a |
|--:|----------------------------|---|
|  1|some long value in this cell|b  |
|  2|medium                      |c  |

Rendered

row	a longer column name	a
1	some long value in this cell	b
2	medium	c

Without padding (new behavior, with is_padding=False)

|row|a longer column name|a|
|--:|---|---|
|1|some long value in this cell|b|
|2|medium|c|

Rendered

row	a longer column name	a
1	some long value in this cell	b
2	medium	c

💭 Other thoughts

1. Should MarkdownTableWriter default to no padding now, in a future (breaking) release, or never?
2. Would it make sense to have a different argument for this behavior? Reference documentation doesn't appear to show parent class properties (is_padding) but it seems like it should? 🤔
3. Would an example in the docs be valuable (e.g., md_example_without_padding.txt)?

Footnotes

1. At least for GitHub Flavored Markdown, and I wasn't able to find anything stating that CommonMark or kramdown require padding for tables. ↩

[Synse]

@thombashi could you take a look at this one? 🙇

[Synse]

@thombashi could you take a look at this PR? 🙇

[thombashi]

Sorry for the delay in reviewing.

1. Should MarkdownTableWriter default to no padding now, in a future (breaking) release, or never?

I don't plan to change the default value.
This is because padding generally improves readability, and changing it would break backward compatibility.

2. Would it make sense to have a different argument for this behavior? Reference documentation doesn't appear to show parent class properties (is_padding) but it seems like it should? 🤔

Since is_padding is declared as .. py:attribute::, it is intended that it does not appear in the subclass documentation.
Generally, users do not need to modify is_padding in individual writer classes.
Since this PR's changes affect only the MarkdownTableWriter class, it might be better to add a docstring to the Args of the MarkdownTableWriter.write_table method.

3. Would an example in the docs be valuable (e.g., md_example_without_padding.txt)?

It would be helpful for users to include an example of using is_padding=False with MarkdownTableWriter.

[thombashi]

I think it would be best to declare 3 as a constant, such as _MIN_HEADER_SEP_LEN .

[thombashi]

What I'd like to emphasize here is that, whether padding is enabled or disabled, a Markdown separator header must consist of at least 3 characters.

Suggested change

	# columns in a header separator row must have at least one dash
	# using a minimum of three accounts for right and center alignment
	# Columns in a header separator row must contain three or more characters;
	# valid examples include (---, --:, :-:).