Ok, but notice the two warnings:

vstinner@apu$ ./python -m test test_docxmlrpc
Run tests sequentially
0:00:00 load avg: 1.19 [1/1] test_docxmlrpc
/home/vstinner/prog/python/master/Lib/xmlrpc/server.py:791: DeprecationWarning: `formatargspec` is deprecated since Python 3.5. Use `signature` and the `Signature` object directly
  formatvalue=self.formatvalue)
/home/vstinner/prog/python/master/Lib/xmlrpc/server.py:784: DeprecationWarning: `formatargspec` is deprecated since Python 3.5. Use `signature` and the `Signature` object directly
  formatvalue=self.formatvalue

== Tests result: SUCCESS ==

1 test OK.

Total duration: 2 sec 698 ms
Tests result: SUCCESS


Fail:

vstinner@apu$ ./python -Werror -m test -v test_docxmlrpc 
test_annotations (test.test_docxmlrpc.DocXMLRPCHTTPGETServer)
Test that annotations works as expected ... ----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 45060)
Traceback (most recent call last):
  File "/home/vstinner/prog/python/master/Lib/socketserver.py", line 313, in _handle_request_noblock
    self.process_request(request, client_address)
  File "/home/vstinner/prog/python/master/Lib/socketserver.py", line 344, in process_request
    self.finish_request(request, client_address)
  File "/home/vstinner/prog/python/master/Lib/socketserver.py", line 357, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/home/vstinner/prog/python/master/Lib/socketserver.py", line 717, in __init__
    self.handle()
  File "/home/vstinner/prog/python/master/Lib/http/server.py", line 426, in handle
    self.handle_one_request()
  File "/home/vstinner/prog/python/master/Lib/http/server.py", line 414, in handle_one_request
    method()
  File "/home/vstinner/prog/python/master/Lib/xmlrpc/server.py", line 936, in do_GET
    response = self.server.generate_html_documentation().encode('utf-8')
  File "/home/vstinner/prog/python/master/Lib/xmlrpc/server.py", line 910, in generate_html_documentation
    methods
  File "/home/vstinner/prog/python/master/Lib/xmlrpc/server.py", line 828, in docserver
    contents.append(self.docroutine(value, key, funcs=fdict))
  File "/home/vstinner/prog/python/master/Lib/xmlrpc/server.py", line 791, in docroutine
    formatvalue=self.formatvalue)
  File "/home/vstinner/prog/python/master/Lib/inspect.py", line 1225, in formatargspec
    stacklevel=2)
DeprecationWarning: `formatargspec` is deprecated since Python 3.5. Use `signature` and the `Signature` object directly
----------------------------------------
ERROR
(...)
== Tests result: FAILURE ==

1 test failed:
    test_docxmlrpc

Total duration: 3 sec 234 ms
Tests result: FAILURE



It seems like the fix is explained in the error message:

Lib/xmlrpc/server.py, line 791, in docroutine():

DeprecationWarning: `formatargspec` is deprecated since Python 3.5. Use `signature` and the `Signature` object directly

Slightly off topic but while trying to look at the code I can see a space between function name and parenthesis as below. It's not an invalid syntax but it's mentioned as a pet peeve in PEP 8 to not to have space between function name and parenthesis. I did a simple grep and I could some places where even function definitions have spaces as below. It's a trivial thing but just wanted to post it here and might seem like an invalid syntax for someone new fixing it.

# Lib/xmlrpc/server.py

argspec = inspect.formatargspec (

# simple grep and manual scanning with `rg '\w+ \(' | grep -v -E 'if|while|for|except|return' | grep '.py' | less`

Tools/gdb/libpython.py:    def __init__ (self, gdbval):
Tools/gdb/libpython.py:    def to_string (self):
Tools/gdb/libpython.py:def register (obj):
Tools/gdb/libpython.py:register (gdb.current_objfile ())
Tools/gdb/libpython.py:        gdb.Command.__init__ (self,
Tools/gdb/libpython.py:        gdb.Command.__init__ (self,
Tools/gdb/libpython.py:        gdb.Command.__init__ (self,
Tools/gdb/libpython.py:        gdb.Command.__init__ (self,
Tools/gdb/libpython.py:        gdb.Command.__init__ (self,

# Relevant PEP 8 section : https://www.python.org/dev/peps/pep-0008/#pet-peeves

> Immediately before the open parenthesis that starts the argument list of a function call:
> Yes: spam(1)
> No:  spam (1)


Also I think it will be good if a deprecation is made then it has to run the test suite with `-Werror` so that the deprecations are fixed which is slightly subjective though where deprecations are reverted back in a future version for reasons like easy 2to3 porting.

Thanks much for these easy issues and I hope someone takes it up.

I'm willing to try solving this!

> Slightly off topic but while trying to look at the code I can see a space between function name and parenthesis as below. (...)

Usually we don't accept changes which only changes the coding style. One reason is to keep a simple history in Git.

New changeset 35c0809158be7feae4c4f877a08b93baea2d8291 by Victor Stinner (Nicolas Noé) in branch 'master':
bpo-33911: Fixed deprecation warning in xmlrpc.server (GH-7847)
https://github.com/python/cpython/commit/35c0809158be7feae4c4f877a08b93baea2d8291

Python 3.7 is affected as well:

vstinner@apu$ ./python -Werror -m test test_docxmlrpc
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 46636)
Traceback (most recent call last):
  (...)
  File "/home/vstinner/prog/python/3.7/Lib/xmlrpc/server.py", line 828, in docserver
    contents.append(self.docroutine(value, key, funcs=fdict))
  File "/home/vstinner/prog/python/3.7/Lib/xmlrpc/server.py", line 791, in docroutine
    formatvalue=self.formatvalue)
  File "/home/vstinner/prog/python/3.7/Lib/inspect.py", line 1225, in formatargspec
    stacklevel=2)
DeprecationWarning: `formatargspec` is deprecated since Python 3.5. Use `signature` and the `Signature` object directly
----------------------------------------
Warning -- threading._dangling was modified by test_docxmlrpc
  Before: <_weakrefset.WeakSet object at 0x7fc84da8f810>
  After:  <_weakrefset.WeakSet object at 0x7fc84da8f538> 
test test_docxmlrpc failed -- multiple errors occurred; run in verbose mode for details
test_docxmlrpc failed


I generated PR 8294 backport to fix Python 3.7 as well. Since the HTML output is unchanged, IMHO it's safe to backport the change.

In the documentation, inspect.formatargspec() is also deprecated in Python 3.6, but the code doesn't emit a DeprecationWarning. I don't think that it's worth it to backport the change to Python 3.6.

New changeset bbddd667a9087f5cfb9e8f9d81fb6d2f75465ba1 by Victor Stinner (Miss Islington (bot)) in branch '3.7':
bpo-33911: Fixed deprecation warning in xmlrpc.server (GH-7847) (GH-8294)
https://github.com/python/cpython/commit/bbddd667a9087f5cfb9e8f9d81fb6d2f75465ba1

Nicolas Noé: Thank you for your change! I merged it in master, and backported it to Python 3.7.