`keep_blank_values=True` when parsing `request.args`

[simonw]

This code in TableView wouldn't be necessary:

datasette/datasette/views/table.py

Lines 396 to 399 in 492f983

	# Ensure we don't drop anything with an empty value e.g. ?name__exact=
	args = MultiParams(
	urllib.parse.parse_qs(request.query_string, keep_blank_values=True)
	)

If that happened here instead:

datasette/datasette/utils/asgi.py

Lines 98 to 100 in 492f983

	@property
	def args(self):
	return MultiParams(parse_qs(qs=self.query_string))

Originally posted by @simonw in #1518 (comment)

[simonw]

This is technically a backwards-incompatible for any plugins that use request.args - but it's unlikely to break anything. At any rate this needs to happen before Datasette 1.0!

[simonw]

Python documentation for parse_qs: https://docs.python.org/3/library/urllib.parse.html#urllib.parse.parse_qs

The optional argument keep_blank_values is a flag indicating whether blank values in percent-encoded queries should be treated as blank strings. A true value indicates that blanks should be retained as blank strings. The default false value indicates that blank values are to be ignored and treated as if they were not included.

[simonw]

Here's an example of the difference that causes:

>>> import urllib.parse
>>> urllib.parse.parse_qs("foo=bar")
{'foo': ['bar']}
>>> urllib.parse.parse_qs("foo=bar&baz=")
{'foo': ['bar']}
>>> urllib.parse.parse_qs("foo=bar&baz=", keep_blank_values=True)
{'foo': ['bar'], 'baz': ['']}