code: def to_timestamp(self, value):
          
          if isinstance(value, (six.integer_types, float, six.string_types)):
              try:
                  return float(value)
              except ValueError:
                  value = self.datetime_str_to_datetime(value)
  
          if isinstance(value, datetime.datetime):
              return self._datetime_to_timestamp(value)
  
          if value is None:
              try:
                  return float(self.default)
              except:
                  return 0.0
  
          raise exceptions.ValidationError(
              "Unable to convert value: '%s' to timestamp" % value,
              code="invalid_timestamp"
          )
docs: from value to timestamp format(float)