text: import base64
  import json
  import operator
  import re
  import shlex
  
  import sqlparse
  from sqlparse.sql import Identifier, Token, Comparison, Statement
  from sqlparse.tokens import Token as TokenType
  
  from mlflow.entities import RunInfo
  from mlflow.exceptions import MlflowException
  from mlflow.protos.databricks_pb2 import INVALID_PARAMETER_VALUE
  
  import math
  
  from mlflow.store.model_registry.dbmodels.models import SqlRegisteredModel
  
  
  class SearchUtils(object):
      LIKE_OPERATOR = "LIKE"
      ILIKE_OPERATOR = "ILIKE"
      ASC_OPERATOR = "asc"
      DESC_OPERATOR = "desc"
      VALID_ORDER_BY_TAGS = [ASC_OPERATOR, DESC_OPERATOR]
      VALID_METRIC_COMPARATORS = set(['>', '>=', '!=', '=', '<', '<='])
      VALID_PARAM_COMPARATORS = set(['!=', '=', LIKE_OPERATOR, ILIKE_OPERATOR])
      VALID_TAG_COMPARATORS = set(['!=', '=', LIKE_OPERATOR, ILIKE_OPERATOR])
      VALID_STRING_ATTRIBUTE_COMPARATORS = set(['!=', '=', LIKE_OPERATOR, ILIKE_OPERATOR])
      CASE_INSENSITIVE_STRING_COMPARISON_OPERATORS = set([LIKE_OPERATOR, ILIKE_OPERATOR])
      VALID_REGISTERED_MODEL_SEARCH_COMPARATORS = \
          CASE_INSENSITIVE_STRING_COMPARISON_OPERATORS.union({'='})
      VALID_SEARCH_ATTRIBUTE_KEYS = set(RunInfo.get_searchable_attributes())
      VALID_ORDER_BY_ATTRIBUTE_KEYS = set(RunInfo.get_orderable_attributes())
      _METRIC_IDENTIFIER = "metric"
      _ALTERNATE_METRIC_IDENTIFIERS = set(["metrics"])
      _PARAM_IDENTIFIER = "parameter"
      _ALTERNATE_PARAM_IDENTIFIERS = set(["parameters", "param", "params"])
      _TAG_IDENTIFIER = "tag"
      _ALTERNATE_TAG_IDENTIFIERS = set(["tags"])
      _ATTRIBUTE_IDENTIFIER = "attribute"
      _ALTERNATE_ATTRIBUTE_IDENTIFIERS = set(["attr", "attributes", "run"])
      _IDENTIFIERS = [_METRIC_IDENTIFIER, _PARAM_IDENTIFIER, _TAG_IDENTIFIER, _ATTRIBUTE_IDENTIFIER]
      _VALID_IDENTIFIERS = set(_IDENTIFIERS
                               + list(_ALTERNATE_METRIC_IDENTIFIERS)
                               + list(_ALTERNATE_PARAM_IDENTIFIERS)
                               + list(_ALTERNATE_TAG_IDENTIFIERS)
                               + list(_ALTERNATE_ATTRIBUTE_IDENTIFIERS))
      STRING_VALUE_TYPES = set([TokenType.Literal.String.Single])
      NUMERIC_VALUE_TYPES = set([TokenType.Literal.Number.Integer, TokenType.Literal.Number.Float])
      # Registered Models Constants
      ORDER_BY_KEY_TIMESTAMP = "timestamp"
      ORDER_BY_KEY_LAST_UPDATED_TIMESTAMP = "last_updated_timestamp"
      ORDER_BY_KEY_MODEL_NAME = SqlRegisteredModel.name.key
      VALID_ORDER_BY_KEYS_REGISTERED_MODELS = set([ORDER_BY_KEY_TIMESTAMP,
                                                   ORDER_BY_KEY_LAST_UPDATED_TIMESTAMP,
                                                   ORDER_BY_KEY_MODEL_NAME])
      VALID_TIMESTAMP_ORDER_BY_KEYS = set([ORDER_BY_KEY_TIMESTAMP,
                                           ORDER_BY_KEY_LAST_UPDATED_TIMESTAMP])
      # We encourage users to use timestamp for order-by
      RECOMMENDED_ORDER_BY_KEYS_REGISTERED_MODELS = set([ORDER_BY_KEY_MODEL_NAME,
                                                         ORDER_BY_KEY_TIMESTAMP])
  
      filter_ops = {
          '>': operator.gt,
          '>=': operator.ge,
          '=': operator.eq,
          '!=': operator.ne,
          '<=': operator.le,
          '<': operator.lt,
          'LIKE': re.match,
          'ILIKE': re.match
      }
  
      @classmethod
      def get_sql_filter_ops(cls, column, operator):
          sql_filter_ops = {
              'LIKE': column.like,
              'ILIKE': column.ilike
          }
          return sql_filter_ops[operator]
  
      @classmethod
      def _trim_ends(cls, string_value):
          return string_value[1:-1]
  
      @classmethod
      def _is_quoted(cls, value, pattern):
          return len(value) >= 2 and value.startswith(pattern) and value.endswith(pattern)
  
      @classmethod
      def _trim_backticks(cls, entity_type):
          """Remove backticks from identifier like `param`, if they exist."""
          if cls._is_quoted(entity_type, "`"):
              return cls._trim_ends(entity_type)
          return entity_type
  
      @classmethod
      def _strip_quotes(cls, value, expect_quoted_value=False):
          """
          Remove quotes for input string.
          Values of type strings are expected to have quotes.
          Keys containing special characters are also expected to be enclose in quotes.
          """
          if cls._is_quoted(value, "'") or cls._is_quoted(value, '"'):
              return cls._trim_ends(value)
          elif expect_quoted_value:
              raise MlflowException("Parameter value is either not quoted or unidentified quote "
                                    "types used for string value %s. Use either single or double "
                                    "quotes." % value, error_code=INVALID_PARAMETER_VALUE)
          else:
              return value
  
      @classmethod
      def _valid_entity_type(cls, entity_type):
          entity_type = cls._trim_backticks(entity_type)
          if entity_type not in cls._VALID_IDENTIFIERS:
              raise MlflowException("Invalid entity type '%s'. "
                                    "Valid values are %s" % (entity_type, cls._IDENTIFIERS),
                                    error_code=INVALID_PARAMETER_VALUE)
  
          if entity_type in cls._ALTERNATE_PARAM_IDENTIFIERS:
              return cls._PARAM_IDENTIFIER
          elif entity_type in cls._ALTERNATE_METRIC_IDENTIFIERS:
              return cls._METRIC_IDENTIFIER
          elif entity_type in cls._ALTERNATE_TAG_IDENTIFIERS:
              return cls._TAG_IDENTIFIER
          elif entity_type in cls._ALTERNATE_ATTRIBUTE_IDENTIFIERS:
              return cls._ATTRIBUTE_IDENTIFIER
          else:
              # one of ("metric", "parameter", "tag", or "attribute") since it a valid type
              return entity_type
  
      @classmethod
      def _get_identifier(cls, identifier, valid_attributes):
          try:
              entity_type, key = identifier.split(".", 1)
          except ValueError:
              raise MlflowException("Invalid identifier '%s'. Columns should be specified as "
                                    "'attribute.<key>', 'metric.<key>', 'tag.<key>', or "
                                    "'param.'." % identifier,
                                    error_code=INVALID_PARAMETER_VALUE)
          identifier = cls._valid_entity_type(entity_type)
          key = cls._trim_backticks(cls._strip_quotes(key))
          if identifier == cls._ATTRIBUTE_IDENTIFIER and key not in valid_attributes:
              raise MlflowException("Invalid attribute key '{}' specified. Valid keys "
                                    " are '{}'".format(key, valid_attributes))
          return {"type": identifier, "key": key}
  
      @classmethod
      def _get_value(cls, identifier_type, token):
          if identifier_type == cls._METRIC_IDENTIFIER:
              if token.ttype not in cls.NUMERIC_VALUE_TYPES:
                  raise MlflowException("Expected numeric value type for metric. "
                                        "Found {}".format(token.value),
                                        error_code=INVALID_PARAMETER_VALUE)
              return token.value
          elif identifier_type == cls._PARAM_IDENTIFIER or identifier_type == cls._TAG_IDENTIFIER:
              if token.ttype in cls.STRING_VALUE_TYPES or isinstance(token, Identifier):
                  return cls._strip_quotes(token.value, expect_quoted_value=True)
              raise MlflowException("Expected a quoted string value for "
                                    "{identifier_type} (e.g. 'my-value'). Got value "
                                    "{value}".format(identifier_type=identifier_type,
                                                     value=token.value),
                                    error_code=INVALID_PARAMETER_VALUE)
          elif identifier_type == cls._ATTRIBUTE_IDENTIFIER:
              if token.ttype in cls.STRING_VALUE_TYPES or isinstance(token, Identifier):
                  return cls._strip_quotes(token.value, expect_quoted_value=True)
              else:
                  raise MlflowException("Expected a quoted string value for attributes. "
                                        "Got value {value}".format(value=token.value),
                                        error_code=INVALID_PARAMETER_VALUE)
          else:
              # Expected to be either "param" or "metric".
              raise MlflowException("Invalid identifier type. Expected one of "
                                    "{}.".format([cls._METRIC_IDENTIFIER, cls._PARAM_IDENTIFIER]))
  
      @classmethod
      def _validate_comparison(cls, tokens):
          base_error_string = "Invalid comparison clause"
          if len(tokens) != 3:
              raise MlflowException("{}. Expected 3 tokens found {}".format(base_error_string,
                                                                            len(tokens)),
                                    error_code=INVALID_PARAMETER_VALUE)
          if not isinstance(tokens[0], Identifier):
              raise MlflowException("{}. Expected 'Identifier' found '{}'".format(base_error_string,
                                                                                  str(tokens[0])),
                                    error_code=INVALID_PARAMETER_VALUE)
          if not isinstance(tokens[1], Token) and tokens[1].ttype != TokenType.Operator.Comparison:
              raise MlflowException("{}. Expected comparison found '{}'".format(base_error_string,
                                                                                str(tokens[1])),
                                    error_code=INVALID_PARAMETER_VALUE)
          if not isinstance(tokens[2], Token) and \
                  (tokens[2].ttype not in cls.STRING_VALUE_TYPES.union(cls.NUMERIC_VALUE_TYPES) or
                   isinstance(tokens[2], Identifier)):
              raise MlflowException("{}. Expected value token found '{}'".format(base_error_string,
                                                                                 str(tokens[2])),
                                    error_code=INVALID_PARAMETER_VALUE)
  
      @classmethod
      def _get_comparison(cls, comparison):
          stripped_comparison = [token for token in comparison.tokens if not token.is_whitespace]
          cls._validate_comparison(stripped_comparison)
          comp = cls._get_identifier(stripped_comparison[0].value, cls.VALID_SEARCH_ATTRIBUTE_KEYS)
          comp["comparator"] = stripped_comparison[1].value
          comp["value"] = cls._get_value(comp.get("type"), stripped_comparison[2])
          return comp
  
      @classmethod
      def _invalid_statement_token(cls, token):
          if isinstance(token, Comparison):
              return False
          elif token.is_whitespace:
              return False
          elif token.match(ttype=TokenType.Keyword, values=["AND"]):
              return False
          else:
              return True
  
      @classmethod
      def _process_statement(cls, statement):
          # check validity
          invalids = list(filter(cls._invalid_statement_token, statement.tokens))
          if len(invalids) > 0:
              invalid_clauses = ", ".join("'%s'" % token for token in invalids)
              raise MlflowException("Invalid clause(s) in filter string: %s" % invalid_clauses,
                                    error_code=INVALID_PARAMETER_VALUE)
          return [cls._get_comparison(si) for si in statement.tokens if isinstance(si, Comparison)]
  
      @classmethod
      def parse_search_filter(cls, filter_string):
          if not filter_string:
              return []
          try:
              parsed = sqlparse.parse(filter_string)
          except Exception:
              raise MlflowException("Error on parsing filter '%s'" % filter_string,
                                    error_code=INVALID_PARAMETER_VALUE)
          if len(parsed) == 0 or not isinstance(parsed[0], Statement):
              raise MlflowException("Invalid filter '%s'. Could not be parsed." %
                                    filter_string, error_code=INVALID_PARAMETER_VALUE)
          elif len(parsed) > 1:
              raise MlflowException("Search filter contained multiple expression '%s'. "
                                    "Provide AND-ed expression list." % filter_string,
                                    error_code=INVALID_PARAMETER_VALUE)
          return SearchUtils._process_statement(parsed[0])
  
      @classmethod
      def is_metric(cls, key_type, comparator):
          if key_type == cls._METRIC_IDENTIFIER:
              if comparator not in cls.VALID_METRIC_COMPARATORS:
                  raise MlflowException("Invalid comparator '%s' "
                                        "not one of '%s" % (comparator,
                                                            cls.VALID_METRIC_COMPARATORS),
                                        error_code=INVALID_PARAMETER_VALUE)
              return True
          return False
  
      @classmethod
      def is_param(cls, key_type, comparator):
          if key_type == cls._PARAM_IDENTIFIER:
              if comparator not in cls.VALID_PARAM_COMPARATORS:
                  raise MlflowException("Invalid comparator '%s' "
                                        "not one of '%s'" % (comparator, cls.VALID_PARAM_COMPARATORS),
                                        error_code=INVALID_PARAMETER_VALUE)
              return True
          return False
  
      @classmethod
      def is_tag(cls, key_type, comparator):
          if key_type == cls._TAG_IDENTIFIER:
              if comparator not in cls.VALID_TAG_COMPARATORS:
                  raise MlflowException("Invalid comparator '%s' "
                                        "not one of '%s" % (comparator, cls.VALID_TAG_COMPARATORS))
              return True
          return False
  
      @classmethod
      def is_attribute(cls, key_type, comparator):
          if key_type == cls._ATTRIBUTE_IDENTIFIER:
              if comparator not in cls.VALID_STRING_ATTRIBUTE_COMPARATORS:
                  raise MlflowException("Invalid comparator '{}' not one of "
                                        "'{}".format(comparator,
                                                     cls.VALID_STRING_ATTRIBUTE_COMPARATORS))
              return True
          return False
  
      @classmethod
      def _does_run_match_clause(cls, run, sed):
          key_type = sed.get('type')
          key = sed.get('key')
          value = sed.get('value')
          comparator = sed.get('comparator').upper()
  
          if cls.is_metric(key_type, comparator):
              lhs = run.data.metrics.get(key, None)
              value = float(value)
          elif cls.is_param(key_type, comparator):
              lhs = run.data.params.get(key, None)
          elif cls.is_tag(key_type, comparator):
              lhs = run.data.tags.get(key, None)
          elif cls.is_attribute(key_type, comparator):
              lhs = getattr(run.info, key)
          else:
              raise MlflowException("Invalid search expression type '%s'" % key_type,
                                    error_code=INVALID_PARAMETER_VALUE)
          if lhs is None:
              return False
  
          if comparator in cls.CASE_INSENSITIVE_STRING_COMPARISON_OPERATORS:
              # Change value from sql syntax to regex syntax
              if comparator == 'ILIKE':
                  value = value.lower()
                  lhs = lhs.lower()
              if not value.startswith('%'):
                  value = '^' + value
              if not value.endswith('%'):
                  value = value + '$'
              value = value.replace('_', '.').replace('%', '.*')
              return cls.filter_ops.get(comparator)(value, lhs)
  
          elif comparator in cls.filter_ops.keys():
              return cls.filter_ops.get(comparator)(lhs, value)
          else:
              return False
  
      @classmethod
      def filter(cls, runs, filter_string):
          """Filters a set of runs based on a search filter string."""
          if not filter_string:
              return runs
          parsed = cls.parse_search_filter(filter_string)
  
          def run_matches(run):
              return all([cls._does_run_match_clause(run, s) for s in parsed])
  
          return [run for run in runs if run_matches(run)]
  
      @classmethod
      def _validate_order_by_and_generate_token(cls, order_by):
          try:
              parsed = sqlparse.parse(order_by)
          except Exception:
              raise MlflowException("Error on parsing order_by clause '{}'".format(order_by),
                                    error_code=INVALID_PARAMETER_VALUE)
          if len(parsed) != 1 or not isinstance(parsed[0], Statement):
              raise MlflowException("Invalid order_by clause '{}'. Could not be parsed."
                                    .format(order_by),
                                    error_code=INVALID_PARAMETER_VALUE)
          statement = parsed[0]
          if len(statement.tokens) == 1 and isinstance(statement[0], Identifier):
              token_value = statement.tokens[0].value
          elif len(statement.tokens) == 1 and \
                  statement.tokens[0].match(ttype=TokenType.Keyword,
                                            values=[cls.ORDER_BY_KEY_TIMESTAMP]):
              token_value = cls.ORDER_BY_KEY_TIMESTAMP
          elif statement.tokens[0].match(ttype=TokenType.Keyword,
                                         values=[cls.ORDER_BY_KEY_TIMESTAMP])\
                  and all([token.is_whitespace for token in statement.tokens[1:-1]])\
                  and statement.tokens[-1].ttype == TokenType.Keyword.Order:
              token_value = cls.ORDER_BY_KEY_TIMESTAMP + ' ' + statement.tokens[-1].value
          else:
              raise MlflowException("Invalid order_by clause '{}'. Could not be parsed."
                                    .format(order_by),
                                    error_code=INVALID_PARAMETER_VALUE)
          return token_value
  
      @classmethod
      def _parse_order_by_string(cls, order_by):
          token_value = cls._validate_order_by_and_generate_token(order_by)
          is_ascending = True
          tokens = shlex.split(token_value.replace("`", "\""))
          if len(tokens) > 2:
              raise MlflowException("Invalid order_by clause '{}'. Could not be parsed."
                                    .format(order_by),
                                    error_code=INVALID_PARAMETER_VALUE)
          elif len(tokens) == 2:
              order_token = tokens[1].lower()
              if order_token not in cls.VALID_ORDER_BY_TAGS:
                  raise MlflowException("Invalid ordering key in order_by clause '{}'."
                                        .format(order_by),
                                        error_code=INVALID_PARAMETER_VALUE)
              is_ascending = (order_token == cls.ASC_OPERATOR)
              token_value = tokens[0]
          return token_value, is_ascending
  
      @classmethod
      def parse_order_by_for_search_runs(cls, order_by):
          token_value, is_ascending = cls._parse_order_by_string(order_by)
          identifier = cls._get_identifier(token_value.strip(), cls.VALID_ORDER_BY_ATTRIBUTE_KEYS)
          return identifier["type"], identifier["key"], is_ascending
  
      @classmethod
      def parse_order_by_for_search_registered_models(cls, order_by):
          token_value, is_ascending = cls._parse_order_by_string(order_by)
          token_value = token_value.strip()
          if token_value not in cls.VALID_ORDER_BY_KEYS_REGISTERED_MODELS:
              raise MlflowException("Invalid order by key '{}' specified. Valid keys "
                                    .format(token_value) +
                                    "are '{}'"
                                    .format(cls.RECOMMENDED_ORDER_BY_KEYS_REGISTERED_MODELS),
                                    error_code=INVALID_PARAMETER_VALUE)
          return token_value, is_ascending
  
      @classmethod
      def _get_value_for_sort(cls, run, key_type, key, ascending):
          """Returns a tuple suitable to be used as a sort key for runs."""
          sort_value = None
          if key_type == cls._METRIC_IDENTIFIER:
              sort_value = run.data.metrics.get(key)
          elif key_type == cls._PARAM_IDENTIFIER:
              sort_value = run.data.params.get(key)
          elif key_type == cls._TAG_IDENTIFIER:
              sort_value = run.data.tags.get(key)
          elif key_type == cls._ATTRIBUTE_IDENTIFIER:
              sort_value = getattr(run.info, key)
          else:
              raise MlflowException("Invalid order_by entity type '%s'" % key_type,
                                    error_code=INVALID_PARAMETER_VALUE)
  
          # Return a key such that None values are always at the end.
          is_null_or_nan = sort_value is None or (isinstance(sort_value, float)
                                                  and math.isnan(sort_value))
          if ascending:
              return (is_null_or_nan, sort_value)
          return (not is_null_or_nan, sort_value)
  
      @classmethod
      def sort(cls, runs, order_by_list):
          """Sorts a set of runs based on their natural ordering and an overriding set of order_bys.
          Runs are naturally ordered first by start time descending, then by run id for tie-breaking.
          """
          runs = sorted(runs, key=lambda run: (-run.info.start_time, run.info.run_uuid))
          if not order_by_list:
              return runs
          # NB: We rely on the stability of Python's sort function, so that we can apply
          # the ordering conditions in reverse order.
          for order_by_clause in reversed(order_by_list):
              (key_type, key, ascending) = cls.parse_order_by_for_search_runs(order_by_clause)
              # pylint: disable=cell-var-from-loop
              runs = sorted(runs,
                            key=lambda run: cls._get_value_for_sort(run, key_type, key, ascending),
                            reverse=not ascending)
          return runs
  
      @classmethod
      def parse_start_offset_from_page_token(cls, page_token):
          # Note: the page_token is expected to be a base64-encoded JSON that looks like
          # { "offset": xxx }. However, this format is not stable, so it should not be
          # relied upon outside of this method.
          if not page_token:
              return 0
  
          try:
              decoded_token = base64.b64decode(page_token)
          except TypeError:
              raise MlflowException("Invalid page token, could not base64-decode",
                                    error_code=INVALID_PARAMETER_VALUE)
          except base64.binascii.Error:
              raise MlflowException("Invalid page token, could not base64-decode",
                                    error_code=INVALID_PARAMETER_VALUE)
  
          try:
              parsed_token = json.loads(decoded_token)
          except ValueError:
              raise MlflowException("Invalid page token, decoded value=%s" % decoded_token,
                                    error_code=INVALID_PARAMETER_VALUE)
  
          offset_str = parsed_token.get("offset")
          if not offset_str:
              raise MlflowException("Invalid page token, parsed value=%s" % parsed_token,
                                    error_code=INVALID_PARAMETER_VALUE)
  
          try:
              offset = int(offset_str)
          except ValueError:
              raise MlflowException("Invalid page token, not stringable %s" % offset_str,
                                    error_code=INVALID_PARAMETER_VALUE)
  
          return offset
  
      @classmethod
      def create_page_token(cls, offset):
          return base64.b64encode(json.dumps({"offset": offset}).encode("utf-8"))
  
      @classmethod
      def paginate(cls, runs, page_token, max_results):
          """Paginates a set of runs based on an offset encoded into the page_token and a max
          results limit. Returns a pair containing the set of paginated runs, followed by
          an optional next_page_token if there are further results that need to be returned.
          """
          start_offset = cls.parse_start_offset_from_page_token(page_token)
          final_offset = start_offset + max_results
  
          paginated_runs = runs[start_offset:final_offset]
          next_page_token = None
          if final_offset < len(runs):
              next_page_token = cls.create_page_token(final_offset)
          return (paginated_runs, next_page_token)
  
      # Model Registry specific parser
      # TODO: Tech debt. Refactor search code into common utils, tracking server, and model
      #       registry specific code.
  
      VALID_SEARCH_KEYS_FOR_MODEL_VERSIONS = set(["name", "run_id", "source_path"])
      VALID_SEARCH_KEYS_FOR_REGISTERED_MODELS = set(["name"])
  
      @classmethod
      def _get_comparison_for_model_registry(cls, comparison, valid_search_keys):
          stripped_comparison = [token for token in comparison.tokens if not token.is_whitespace]
          cls._validate_comparison(stripped_comparison)
          key = stripped_comparison[0].value
          if key not in valid_search_keys:
              raise MlflowException("Invalid attribute key '{}' specified. Valid keys "
                                    " are '{}'".format(key, valid_search_keys),
                                    error_code=INVALID_PARAMETER_VALUE)
          value_token = stripped_comparison[2]
          if value_token.ttype not in cls.STRING_VALUE_TYPES:
              raise MlflowException("Expected a quoted string value for attributes. "
                                    "Got value {value}".format(value=value_token.value),
                                    error_code=INVALID_PARAMETER_VALUE)
          comp = {
              "key": key,
              "comparator": stripped_comparison[1].value,
              "value": cls._strip_quotes(value_token.value, expect_quoted_value=True)
          }
          return comp
  
      @classmethod
      def _parse_filter_for_model_registry(cls, filter_string, valid_search_keys):
          if not filter_string or filter_string == "":
              return []
          expected = "Expected search filter with single comparison operator. e.g. name='myModelName'"
          try:
              parsed = sqlparse.parse(filter_string)
          except Exception:
              raise MlflowException("Error while parsing filter '%s'. %s" % (filter_string, expected),
                                    error_code=INVALID_PARAMETER_VALUE)
          if len(parsed) == 0 or not isinstance(parsed[0], Statement):
              raise MlflowException("Invalid filter '%s'. Could not be parsed. %s" %
                                    (filter_string, expected), error_code=INVALID_PARAMETER_VALUE)
          elif len(parsed) > 1:
              raise MlflowException("Search filter '%s' contains multiple expressions. "
                                    "%s " % (filter_string, expected),
                                    error_code=INVALID_PARAMETER_VALUE)
          statement = parsed[0]
          invalids = list(filter(cls._invalid_statement_token, statement.tokens))
          if len(invalids) > 0:
              invalid_clauses = ", ".join("'%s'" % token for token in invalids)
              raise MlflowException("Invalid clause(s) in filter string: %s. "
                                    "%s" % (invalid_clauses, expected),
                                    error_code=INVALID_PARAMETER_VALUE)
          return [cls._get_comparison_for_model_registry(
              si,
              valid_search_keys)
              for si in statement.tokens if isinstance(si, Comparison)]
  
      @classmethod
      def parse_filter_for_model_versions(cls, filter_string):
          return cls._parse_filter_for_model_registry(
              filter_string,
              cls.VALID_SEARCH_KEYS_FOR_MODEL_VERSIONS)
  
      @classmethod
      def parse_filter_for_registered_models(cls, filter_string):
          return cls._parse_filter_for_model_registry(
              filter_string,
              cls.VALID_SEARCH_KEYS_FOR_REGISTERED_MODELS)
  