twistd -n dns fails on Python 3

[twisted-trac]

	@rodrigc reported
Trac ID	trac#9783
Type	defect
Created	2020-03-24 17:51:20Z

I tried this example: https://twisted.readthedocs.io/en/twisted-18.9.0/names/howto/names.html#creating-an-authoritative-server

Using:

Twisted: 20.3.0
Python: 3.7

and it failed with:

Traceback (most recent call last):
  File "/Users/craigrodrigues/twisted-venv/lib/python3.7/site-packages/twisted/names/tap.py", line 95, in postOptions
    self.zones.append(authority.PySourceAuthority(f))
  File "/Users/craigrodrigues/twisted-venv/lib/python3.7/site-packages/twisted/names/authority.py", line 90, in __init__
    self.loadFile(filename)
  File "/Users/craigrodrigues/twisted-venv/lib/python3.7/site-packages/twisted/names/authority.py", line 290, in loadFile
    g, l = self.setupConfigNamespace(), {}
  File "/Users/craigrodrigues/twisted-venv/lib/python3.7/site-packages/twisted/names/authority.py", line 308, in setupConfigNamespace
    items = dns.__dict__.iterkeys()

Searchable metadata

trac-id__9783 9783
type__defect defect
reporter__rodrigc rodrigc
priority__normal normal
milestone__Python_3_x Python-3.x
branch__ 
branch_author__ 
status__closed closed
resolution__fixed fixed
component__names names
keywords__None None
time__1585072280055419 1585072280055419
changetime__1585165266607937 1585165266607937
version__None None
owner__rodrigc rodrigc

[twisted-trac]

	@rodrigc commented

#1233

[twisted-trac]

	@rodrigc set owner to @rodrigc

Approved by twm: #1233 (review)

[twisted-trac]

	@rodrigc set status to closed

In changeset 1ffda84

#!CommitTicketReference repository="" revision="1ffda84cbb7165172d53adcb687a9359ff6fdd07"
Merge pull request #1233 from twisted/9783-rodrigc-names

Change iterkeys() to keys(), since iterkeys() does not exist in Python 3

Author: rodrigc
Reviewer: twm
Fixes: ticket:9783