code: def preview_from_config(name, url, backend,
                          description=None,
                          frequency=DEFAULT_HARVEST_FREQUENCY,
                          owner=None,
                          organization=None,
                          config=None,
                          ):
      '''Preview an harvesting from a source created with the given parameters'''
      if owner and not isinstance(owner, User):
          owner = User.get(owner)
  
      if organization and not isinstance(organization, Organization):
          organization = Organization.get(organization)
  
      source = HarvestSource(
          name=name,
          url=url,
          backend=backend,
          description=description,
          frequency=frequency or DEFAULT_HARVEST_FREQUENCY,
          owner=owner,
          organization=organization,
          config=config,
      )
      cls = backends.get(current_app, source.backend)
      max_items = current_app.config['HARVEST_PREVIEW_MAX_ITEMS']
      backend = cls(source, dryrun=True, max_items=max_items)
      return backend.harvest(f preview_from_config(name, url, backend,
                          description=None,
                          frequency=DEFAULT_HARVEST_FREQUENCY,
                          owner=None,
                          organization=None,
                          config=None,
                          ):
      '''Preview an harvesting from a source created with the given parameters'''
      if owner and not isinstance(owner, User):
          owner = User.get(owner)
  
      if organization and not isinstance(organization, Organization):
          organization = Organization.get(organization)
  
      source = HarvestSource(
          name=name,
          url=url,
          backend=backend,
          description=description,
          frequency=frequency or DEFAULT_HARVEST_FREQUENCY,
          owner=owner,
          organization=organization,
          config=config,
      )
      cls = backends.get(current_app, source.backend)
      max_items = current_app.config['HARVEST_PREVIEW_MAX_ITEMS']
      backend = cls(source, dryrun=True, max_items=max_items)
      return backend.harvest()
docs: Preview an harvesting from a source created with the given parameters