A quick hack (needs package python3-launchpadlib):

#!/usr/bin/python3

# -*- coding: utf-8 -*-



import sys,re



from launchpadlib.launchpad import Launchpad

import httplib2

import  lazr.restfulclient.errors



if len(sys.argv) < 2:

    print('Syntax: {cmd} ppa'.format(cmd=sys.argv[0]))

    print()

    print('For example: {cmd}  ppa://diesch/testing'.format(cmd=sys.argv[0]))

    sys.exit(2)





try:

    lp = Launchpad.login_anonymously('foo', 'production', None)

except  httplib2.HttpLib2Error as e:

    print('Error connection to launchpad.net:', e)

    sys.exit(1)





ppa_name = sys.argv[1].strip()



m = re.search(r'^(ppa:)?(?P<user>[^/]+)/(?P<name>.+)', ppa_name)

if m:

    user, name = m.group('user', 'name')

else:

    print('Unvalid PPA name:', ppa)

    sys.exit(1)



try:    

    owner =  lp.people[user]

    ppa = owner.getPPAByName(name=name)



    print('PPA {name} at {url}'.format(name=ppa_name, url=ppa.web_link))

    print()

    print('Owner: {owner} ({url})'.format(owner=owner.display_name,

                                            url=owner.web_link))

    print()

    print(ppa.description) 

except lazr.restfulclient.errors.RestfulError as e:

    print('Error getting PPA info:', e)

    exit(1)

Save this as e.g. ppa-info, make it executable and run it like

ppa-info ppa:diesch/testing

If the PPA exists, you will get some information, like owner and description, otherwise you'll get an error message.