web.py release: 0.40
Python release: 3.7.3 (Debian buster)

While porting a project from Python 2 to Python 3 (thanks for the 0.40 release!), I immediately encountered a bug in web.input(). Apparently, when a POST is sent by requests (as opposed to a web browser), web.py emits an error:

TypeError: write() argument must be str, not bytes

If debug is enabled, the default, then a stream of errors occur with the a similar error. See this issue for more information #448.

Sure enough, setting web.config.debug = False will prevent the stream of errors, yet the originating error still exists. (Also, I want error handling, I'll address that later).

The source of the error is in cgi.py, as it tries and copy the BytesIO object web.py created into a TemporaryFile that was created without wb+.

Here is the cgi.py write error:
https://github.com/python/cpython/blob/ef4ec6ed12d6c6200a85068f60483723298b6ff4/Lib/cgi.py#L704

Here is the web.py BytesIO creation:

I am able fix this by monkey patching cgi.py, as the source of the error is make_file:
https://github.com/python/cpython/blob/ef4ec6ed12d6c6200a85068f60483723298b6ff4/Lib/cgi.py#L814-L842

Here is a test case:

import cgi
import web
import json
import tempfile

urls = (
    '/', 'index'
)

class index:
    def POST(self):
        inputs = web.input()
        data = json.loads(web.data())
        print(inputs, data)
        return "Hello, world!"

def make_file(self):
    return tempfile.TemporaryFile("wb+")

# Comment out this line to reproduce the error                                                                                                                               
cgi.FieldStorage.make_file = make_file

if __name__ == "__main__":
    # Comment this line to see the stream of errors. Note, make_file
    # also needs to be the default, not patched, version.
    web.config.debug = False
    app = web.application(urls, globals())
    app.run()

You may test this with httpie:

$ http -v POST localhost:8080 a=b

One last comment, when monkey patching cgi.py, the debugging error page works again.

Is there anything else I can submit to help solve this?