text: # MySQL Connector/Python - MySQL driver written in Python.
  
  
  import re
  from collections import namedtuple
  
  import django
  
  if django.VERSION >= (1, 8):
      from django.db.backends.base.introspection import (
          BaseDatabaseIntrospection, FieldInfo, TableInfo
      )
  else:
      from django.db.backends import BaseDatabaseIntrospection
  
  if django.VERSION >= (1, 6):
      if django.VERSION < (1, 8):
          from django.db.backends import FieldInfo
      from django.utils.encoding import force_text
  
      if django.VERSION >= (1, 7):
          from django.utils.datastructures import OrderedSet
  
  from PyMysqlPool.mysql.connector.constants import FieldType
  
  foreign_key_re = re.compile(r"\sCONSTRAINT `[^`]*` FOREIGN KEY \(`([^`]*)`\) "
                              r"REFERENCES `([^`]*)` \(`([^`]*)`\)")
  
  if django.VERSION >= (1, 8):
      FieldInfo = namedtuple('FieldInfo', FieldInfo._fields + ('extra',))
  
  
  class DatabaseIntrospection(BaseDatabaseIntrospection):
      data_types_reverse = {
          FieldType.BLOB: 'TextField',
          FieldType.DECIMAL: 'DecimalField',
          FieldType.NEWDECIMAL: 'DecimalField',
          FieldType.DATE: 'DateField',
          FieldType.DATETIME: 'DateTimeField',
          FieldType.DOUBLE: 'FloatField',
          FieldType.FLOAT: 'FloatField',
          FieldType.INT24: 'IntegerField',
          FieldType.LONG: 'IntegerField',
          FieldType.LONGLONG: 'BigIntegerField',
          FieldType.SHORT: (
              'IntegerField' if django.VERSION < (1, 8) else 'SmallIntegerField'
          ),
          FieldType.STRING: 'CharField',
          FieldType.TIME: 'TimeField',
          FieldType.TIMESTAMP: 'DateTimeField',
          FieldType.TINY: 'IntegerField',
          FieldType.TINY_BLOB: 'TextField',
          FieldType.MEDIUM_BLOB: 'TextField',
          FieldType.LONG_BLOB: 'TextField',
          FieldType.VAR_STRING: 'CharField',
      }
  
      def get_field_type(self, data_type, description):
          field_type = super(DatabaseIntrospection, self).get_field_type(
              data_type, description)
          if (field_type == 'IntegerField'
              and 'auto_increment' in description.extra):
              return 'AutoField'
          return field_type
  
      def get_table_list(self, cursor):
          """Returns a list of table names in the current database."""
          cursor.execute("SHOW FULL TABLES")
          if django.VERSION >= (1, 8):
              return [
                  TableInfo(row[0], {'BASE TABLE': 't', 'VIEW': 'v'}.get(row[1]))
                  for row in cursor.fetchall()
                  ]
          else:
              return [row[0] for row in cursor.fetchall()]
  
      if django.VERSION >= (1, 8):
          def get_table_description(self, cursor, table_name):
              """
              Returns a description of the table, with the DB-API
              cursor.description interface."
              """
              # - information_schema database gives more accurate results for
              #   some figures:
              # - varchar length returned by cursor.description is an internal
              #   length, not visible length (#5725)
              # - precision and scale (for decimal fields) (#5014)
              # - auto_increment is not available in cursor.description
              InfoLine = namedtuple(
                  'InfoLine',
                  'col_name data_type max_len num_prec num_scale extra'
              )
              cursor.execute("""
                  SELECT column_name, data_type, character_maximum_length,
                  numeric_precision, numeric_scale, extra
                  FROM information_schema.columns
                  WHERE table_name = %s AND table_schema = DATABASE()""",
                             [table_name])
              field_info = dict(
                  (line[0], InfoLine(*line)) for line in cursor.fetchall()
              )
  
              cursor.execute("SELECT * FROM %s LIMIT 1"
                             % self.connection.ops.quote_name(table_name))
              to_int = lambda i: int(i) if i is not None else i
              fields = []
              for line in cursor.description:
                  col_name = force_text(line[0])
                  fields.append(
                      FieldInfo(*((col_name,)
                                  + line[1:3]
                                  + (to_int(field_info[col_name].max_len)
                                     or line[3],
                                     to_int(field_info[col_name].num_prec)
                                     or line[4],
                                     to_int(field_info[col_name].num_scale)
                                     or line[5])
                                  + (line[6],)
                                  + (field_info[col_name].extra,)))
                  )
              return fields
      else:
          def get_table_description(self, cursor, table_name):
              """
              Returns a description of the table, with the DB-API
              cursor.description interface.
              """
              # varchar length returned by cursor.description is an internal
              # length not visible length (#5725), use information_schema database
              #  to fix this
              cursor.execute(
                  "SELECT column_name, character_maximum_length "
                  "FROM INFORMATION_SCHEMA.COLUMNS "
                  "WHERE table_name = %s AND table_schema = DATABASE() "
                  "AND character_maximum_length IS NOT NULL", [table_name])
              length_map = dict(cursor.fetchall())
  
              # Also getting precision and scale from
              # information_schema (see #5014)
              cursor.execute(
                  "SELECT column_name, numeric_precision, numeric_scale FROM "
                  "INFORMATION_SCHEMA.COLUMNS WHERE table_name = %s AND "
                  "table_schema = DATABASE() AND data_type='decimal'",
                  [table_name])
              numeric_map = dict((line[0], tuple([int(n) for n in line[1:]]))
                                 for line in cursor.fetchall())
  
              cursor.execute("SELECT * FROM {0} LIMIT 1".format(
                  self.connection.ops.quote_name(table_name)))
  
              if django.VERSION >= (1, 6):
                  return [FieldInfo(*((force_text(line[0]),)
                                      + line[1:3]
                                      + (length_map.get(line[0], line[3]),)
                                      + numeric_map.get(line[0], line[4:6])
                                      + (line[6],)))
                          for line in cursor.description]
              else:
                  return [
                      line[:3] + (length_map.get(line[0], line[3]),) + line[4:]
                      for line in cursor.description
                      ]
  
      def _name_to_index(self, cursor, table_name):
          """
          Returns a dictionary of {field_name: field_index} for the given table.
          Indexes are 0-based.
          """
          return dict((d[0], i) for i, d in enumerate(
              self.get_table_description(cursor, table_name)))
  
      def get_relations(self, cursor, table_name):
          """
          Returns a dictionary of {field_index: (field_index_other_table,
          other_table)}
          representing all relationships to the given table. Indexes are 0-based.
          """
          constraints = self.get_key_columns(cursor, table_name)
          relations = {}
          if django.VERSION >= (1, 8):
              for my_fieldname, other_table, other_field in constraints:
                  relations[my_fieldname] = (other_field, other_table)
              return relations
          else:
              my_field_dict = self._name_to_index(cursor, table_name)
              for my_fieldname, other_table, other_field in constraints:
                  other_field_index = self._name_to_index(
                      cursor, other_table)[other_field]
                  my_field_index = my_field_dict[my_fieldname]
                  relations[my_field_index] = (other_field_index, other_table)
              return relations
  
      def get_key_columns(self, cursor, table_name):
          """
          Returns a list of (column_name, referenced_table_name,
          referenced_column_name) for all key columns in given table.
          """
          key_columns = []
          cursor.execute(
              "SELECT column_name, referenced_table_name, referenced_column_name "
              "FROM information_schema.key_column_usage "
              "WHERE table_name = %s "
              "AND table_schema = DATABASE() "
              "AND referenced_table_name IS NOT NULL "
              "AND referenced_column_name IS NOT NULL", [table_name])
          key_columns.extend(cursor.fetchall())
          return key_columns
  
      def get_indexes(self, cursor, table_name):
          cursor.execute("SHOW INDEX FROM {0}"
                         "".format(self.connection.ops.quote_name(table_name)))
          # Do a two-pass search for indexes: on first pass check which indexes
          # are multicolumn, on second pass check which single-column indexes
          # are present.
          rows = list(cursor.fetchall())
          multicol_indexes = set()
          for row in rows:
              if row[3] > 1:
                  multicol_indexes.add(row[2])
          indexes = {}
          for row in rows:
              if row[2] in multicol_indexes:
                  continue
              if row[4] not in indexes:
                  indexes[row[4]] = {'primary_key': False, 'unique': False}
              # It's possible to have the unique and PK constraints in
              # separate indexes.
              if row[2] == 'PRIMARY':
                  indexes[row[4]]['primary_key'] = True
              if not row[1]:
                  indexes[row[4]]['unique'] = True
          return indexes
  
      def get_primary_key_column(self, cursor, table_name):
          """
          Returns the name of the primary key column for the given table
          """
          # Django 1.6
          for column in self.get_indexes(cursor, table_name).items():
              if column[1]['primary_key']:
                  return column[0]
          return None
  
      def get_storage_engine(self, cursor, table_name):
          """
          Retrieves the storage engine for a given table. Returns the default
          storage engine if the table doesn't exist.
          """
          cursor.execute(
              "SELECT engine "
              "FROM information_schema.tables "
              "WHERE table_name = %s", [table_name])
          result = cursor.fetchone()
          if not result:
              return self.connection.features.mysql_storage_engine
          return result[0]
  
      def get_constraints(self, cursor, table_name):
          """
          Retrieves any constraints or keys (unique, pk, fk, check, index) across
          one or more columns.
          """
          # Django 1.7
          constraints = {}
          # Get the actual constraint names and columns
          name_query = (
              "SELECT kc.`constraint_name`, kc.`column_name`, "
              "kc.`referenced_table_name`, kc.`referenced_column_name` "
              "FROM information_schema.key_column_usage AS kc "
              "WHERE "
              "kc.table_schema = %s AND "
              "kc.table_name = %s"
          )
          cursor.execute(name_query, [self.connection.settings_dict['NAME'],
                                      table_name])
          for constraint, column, ref_table, ref_column in cursor.fetchall():
              if constraint not in constraints:
                  constraints[constraint] = {
                      'columns': OrderedSet(),
                      'primary_key': False,
                      'unique': False,
                      'index': False,
                      'check': False,
                      'foreign_key': (
                          (ref_table, ref_column) if ref_column else None,
                      )
                  }
              constraints[constraint]['columns'].add(column)
          # Now get the constraint types
          type_query = """
              SELECT c.constraint_name, c.constraint_type
              FROM information_schema.table_constraints AS c
              WHERE
                  c.table_schema = %s AND
                  c.table_name = %s
          """
          cursor.execute(type_query, [self.connection.settings_dict['NAME'],
                                      table_name])
          for constraint, kind in cursor.fetchall():
              if kind.lower() == "primary key":
                  constraints[constraint]['primary_key'] = True
                  constraints[constraint]['unique'] = True
              elif kind.lower() == "unique":
                  constraints[constraint]['unique'] = True
          # Now add in the indexes
          cursor.execute("SHOW INDEX FROM %s" % self.connection.ops.quote_name(
              table_name))
          for table, non_unique, index, colseq, column in [x[:5] for x in
                                                           cursor.fetchall()]:
              if index not in constraints:
                  constraints[index] = {
                      'columns': OrderedSet(),
                      'primary_key': False,
                      'unique': False,
                      'index': True,
                      'check': False,
                      'foreign_key': None,
                  }
              constraints[index]['index'] = True
              constraints[index]['columns'].add(column)
          # Convert the sorted sets to lists
          for constraint in constraints.values():
              constraint['columns'] = list(constraint['columns'])
          return constraints
  