async attribute in python 3.7+

[Alexei Martchenko]

Async is a reserved word in Python 3.7. Thus, it cannot be used as argument.

This code works perfectly in Python 2.7 (and 3.2 to 3.6 I believe) but not in 3.7.6

>>> from bs4 import BeautifulSoup
>>> soup = BeautifulSoup('<p>test</p>')
>>> new_tag = soup.new_tag('script', async=None, src="https://platform.twitter.com/widgets.js",charset="utf-8")
  File "<stdin>", line 1
    new_tag = soup.new_tag('script', async=None, src="https://platform.twitter.com/widgets.js",charset="utf-8")
                                         ^
SyntaxError: invalid syntax

Should BS4 use _async like _class?

[Leonard Richardson (leonardr)]

Thanks for taking the time to file this issue.

'class' gets special treatment in find() and similar methods because CSS class is the single most common way people look for a tag. It doesn't get special treatment in new_tag(), and 'async' is much less common, so my recommendation is to use the 'attrs' argument instead of Python keyword arguments:

new_tag = soup.new_tag('script', attrs={'async': None}, src="https://platform.twitter.com/widgets.js", charset="utf-8")

In revision 574 I improved the new_tag() docstring to mention this possibility.