issue_comments

I bet this is because I'm mucking around with one of those __ methods. I'll try just doing the non-underscore methods instead.

Here's the output of dir(str):

['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isascii', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

It looks like this is specific to the way PrefixedUrlString is built. (Pdb) class Weird(str): pass (Pdb) isinstance(Weird('bob'), collections.abc.Awaitable) False So subclassing strings doesn't trigger this bug, but something about PrefixedUrlString causes the problem.

Here's the current PrefixedUrlString implementation:

https://github.com/simonw/datasette/blob/bf18b9ba175a7b25fb8b765847397dd6efb8bb7b/datasette/utils/init.py#L1015-L1035

Here's the core problem: (Pdb) isinstance('bob', collections.abc.Awaitable) False (Pdb) isinstance(PrefixedUrlString('bob'), collections.abc.Awaitable) *** TypeError: issubclass() arg 1 must be a class For some reason isinstance() does not like being handed an instance of PrefixedUrlString.

I wonder how Jinja's Markup() class works? It uses https://pypi.org/project/MarkupSafe/

It's a subclass of str, defined here: https://github.com/pallets/markupsafe/blob/master/src/markupsafe/init.py

Sample traceback: ``` <link rel="stylesheet" href="{{ urls.static('app.css') }}?{{ app_css_hash }}"> /opt/hostedtoolcache/Python/3.7.9/x64/lib/python3.7/site-packages/jinja2/asyncsupport.py:173: in auto_await if inspect.isawaitable(value): /opt/hostedtoolcache/Python/3.7.9/x64/lib/python3.7/inspect.py:226: in isawaitable isinstance(object, collections.abc.Awaitable)) /opt/hostedtoolcache/Python/3.7.9/x64/lib/python3.7/abc.py:139: in instancecheck return _abc_instancecheck(cls, instance)

cls = <class 'collections.abc.Awaitable'> subclass = <bound method PrefixedUrlString.__getattribute__.\<locals>.method of '/-/static/app.css'>

def __subclasscheck__(cls, subclass):
    """Override for issubclass(subclass, cls)."""

  return _abc_subclasscheck(cls, subclass)

E TypeError: issubclass() arg 1 must be a class `` This is within Jinja. It looks like Jinja really doesn't like methods that return non-string objects likePrefixedUrlString`.