def check_field(vglist,key,value):
  """
  Accepts a list of dicts; for each dict, check the the specified key contains the specified value.
  """
  for row in vglist:
    assert row[key] == value, \
      '** Error: Field: %s contains value: %s, expected: %s' % (str(key),str(row[key]),str(value))
  return True