How to use the nvchecker.core.Source function in nvchecker

def take():
  parser = argparse.ArgumentParser(description='update version records of nvchecker')
  core.add_common_arguments(parser)
  parser.add_argument('--all', action='store_true',
                      help='take all updates')
  parser.add_argument('--ignore-nonexistent', action='store_true',
                      help='ignore nonexistent names')
  parser.add_argument('names', metavar='NAME', nargs='*',
                      help='software name to be updated')
  args = parser.parse_args()
  if core.process_common_arguments(args):
    return

  s = core.Source(args.file)
  if not s.oldver or not s.newver:
    logger.critical(
      "doesn't have both 'oldver' and 'newver' set.", source=s,
    )
    sys.exit(2)

  oldvers = core.read_verfile(s.oldver)
  newvers = core.read_verfile(s.newver)

  if args.all:
    oldvers.update(newvers)
  else:
    for name in args.names:
      try:
        oldvers[name] = newvers[name]
      except KeyError:

# Copyright (c) 2013-2017 lilydjwg , et al.

import argparse
import asyncio

import structlog

from .lib import notify
from . import core

logger = structlog.get_logger(logger_name=__name__)

notifications = []
args = None

class Source(core.Source):
  def on_update(self, name, version, oldver):
    if args.notify:
      msg = '%s updated to version %s' % (name, version)
      notifications.append(msg)
      notify.update('nvchecker', '\n'.join(notifications))

def main():
  global args

  parser = argparse.ArgumentParser(description='New version checker for software')
  parser.add_argument('-n', '--notify', action='store_true', default=False,
                      help='show desktop notifications when a new version is available')
  parser.add_argument('-t', '--tries', default=1, type=int, metavar='N',
                      help='try N times when errors occur')
  core.add_common_arguments(parser)
  args = parser.parse_args()

def cmp():
  parser = argparse.ArgumentParser(description='compare version records of nvchecker')
  core.add_common_arguments(parser)
  args = parser.parse_args()
  if core.process_common_arguments(args):
    return

  s = core.Source(args.file)
  oldvers = core.read_verfile(s.oldver) if s.oldver else {}
  newvers = core.read_verfile(s.newver)
  for name, newver in sorted(newvers.items()):
    oldver = oldvers.get(name, None)
    if oldver != newver:
      print('%s %s -> %s' % (name, oldver, newver))