what's the meaning of attr "xsi_type" in python

[liuwe...@gmail.com]

hi AdWords API Team,what's the meaning of attr "xsi_type" in python,I can't find any info in reference

# Construct keyword ad group criterion object.
  keyword1 = {
      'xsi_type': 'BiddableAdGroupCriterion',
      'adGroupId': ad_group_id,
      'criterion': {
          'xsi_type': 'Keyword',
          'matchType': 'BROAD',
          'text': 'mars'
      },
      # These fields are optional.
      'userStatus': 'PAUSED',
      'finalUrls': {
          'urls': ['http://example.com/mars']
      }
  }

  keyword2 = {
      'xsi_type': 'NegativeAdGroupCriterion',
      'adGroupId': ad_group_id,
      'criterion': {
          'xsi_type': 'Keyword',
          'matchType': 'EXACT',
          'text': 'pluto'
      }
  }

[liuwe...@gmail.com]

[Dhanya Sundararaju (AdWords API Team)]

Hi there,

The xsi_type is the Type of object that you specify when you run operations for a service. For example, in your screenshot, to add a keyword in AdGroup, you will need to call the AdGroupCriterionService, then, add an object of Type BiddableAdGroupCriterion or NegativeAdGroupCriterion. Then, to those objects you will need to add an object of Type Keyword where you will specify the text and matchtype. Please let me know if you have any further questions.

Regards,
Dhanya, AdWords API Team