Log Message:
py-beautifulsoup4: updated to 4.9.1

4.9.1:

* Added a keyword argument 'on_duplicate_attribute' to the
  BeautifulSoupHTMLParser constructor (used by the html.parser tree
  builder) which lets you customize the handling of markup that
  contains the same attribute more than once, as in:
  <a href="url1" href="url2">

* Added a distinct subclass, GuessedAtParserWarning, for the warning
  issued when BeautifulSoup is instantiated without a parser being
  specified.

* Added a distinct subclass, MarkupResemblesLocatorWarning, for the
  warning issued when BeautifulSoup is instantiated with 'markup' that
  actually seems to be a URL or the path to a file on
  disk.

* The new NavigableString subclasses (Stylesheet, Script, and
  TemplateString) can now be imported directly from the bs4 package.

* If you encode a document with a Python-specific encoding like
  'unicode_escape', that encoding is no longer mentioned in the final
  XML or HTML document. Instead, encoding information is omitted or
  left blank.

* Fixed test failures when run against soupselect 2.0.