python db class usage description

import pymysql
 
class DB:
 __host = 'localhost' # Server address
 __username = 'root' # Username
 __password = '' # Password
 __database = 'test' # Database
 __field = '*' # Query Fields
 __where = '' # Conditions
 __sql = False # Whether to return sql
 __join = '' # Joint tables
 __order = '' # Sort
 __limit = '' # Quantity
 
 # constructor, called when generating the object
 def __init__(self, table):
  try:
   # Open a database connection host, username, password, database
    = (self.__host, self.__username, self.__password, self.__database)
  except Exception as e:
   print(e)
   exit()
 
  # Use the cursor() method to create a cursor object cursor
   = ()
   = table
 
 # Deconstructor function, used when releasing an object
 def __del__(self):
  try:
   # Close the database connection
   ()
  except Exception as e:
   print(e)
 
 # Get the current sql statement
 def getSql(self):
  self.__sql = True
  return self
 
 # field
 def field(self, str):
  self.__field = str
  return self
 
 # Joint tables
 def join(self, table, where):
  self.__join = ' LEFT JOIN ' + table + ' ON ' + where + ' '
  return self
 
 # Conditions
 def where(self, param):
  self.__where = ' WHERE '
  if isinstance(param, list):
   for i in param:
    if isinstance(i[2], list):
     tmp = '('
     for j in i[2]:
      tmp += str(j) + ','
     tmp += ')'
     self.__where += '`' + i[0] + '` ' + i[1] + ' ' + tmp + ' AND '
    else:
     self.__where += '`' + i[0] + '` ' + i[1] + ' ' + str(i[2]) + ' AND '
   else:
    self.__where = self.__where[0:-4]
  else:
   self.__where += param
 
  return self
 
 # Sort
 def order(self, str):
  self.__order = ' ORDER BY ' + str
  return self
 
 # Quantity
 def limit(self, str):
  self.__limit = ' LIMIT ' + str
  return self
 
 # Increase
 def insert(self, dict):
  key = value = ''
  for k, v in ():
   key += '`' + k + '`,'
   value += '"' + v + '",'
 
  key = key[0:-1]
  value = value[0:-1]
 
  sql = 'INSERT INTO ' +  + ' (' + key + ') VALUES (' + value + ')'
  if self.__sql:
   return sql
 
  try:
   # Execute sql statements
   ret = (sql)
   # Submitted to database for execution
   ()
   return ret
  except Exception as e:
   # Rollback if an error occurs
   ()
   print(e)
   return 0
 
 # Delete
 def delete(self):
  if self.__where:
   sql = "DELETE FROM " +  + self.__where
   if self.__sql:
    return sql
 
   try:
    # Execute sql statements
    ret = (sql)
    # Submitted to database for execution
    ()
    return ret
   except Exception as e:
    # Rollback if an error occurs
    ()
    print(e)
    return 0
 
  else:
   raise BaseException('No conditions') # Throwing exceptions
 
 # Modify
 def update(self, dict):
  str = ''
  for k, v in ():
   str += '`' + k + '`="' + v + '",'
 
  str = str[0:-1]
  sql = 'UPDATE ' +  + ' SET ' + str
 
  if self.__where:
   sql += self.__where
  if self.__sql:
   return sql
 
  try:
   # Execute sql statements
   ret = (sql)
   # Submitted to database for execution
   ()
   return ret
  except Exception as e:
   # Rollback if an error occurs
   ()
   print(e)
   return 0
 
 # Query
 def select(self):
  sql = "SELECT " + self.__field + " FROM " + 
 
  if self.__join:
   sql += self.__join
 
  if self.__where:
   sql += self.__where
 
  if self.__order:
   sql += self.__order
 
  if self.__limit:
   sql += self.__limit
 
  if self.__sql:
   return sql
 
  # Execute SQL queries using the execute() method
  (sql)
 
  # Use the fetchall() method to get all the data.
  data = ()
  return data
'''
DROP TABLE IF EXISTS `people`;
CREATE TABLE `people` (
 `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
 `name` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL COMMENT 'Name',
 `sex` varchar(7) DEFAULT '' COMMENT 'distinguishing between the sexes',
 `job` varchar(6) DEFAULT '' COMMENT '(of a machine) operate',
 `age` varchar(6) DEFAULT '' COMMENT '(a person's) age',
 `height` varchar(6) DEFAULT '' COMMENT '(a person's) height',
 `weight` varchar(6) DEFAULT '' COMMENT 'weight',
 PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
INSERT INTO `people` VALUES ('1', 'Zhao Yi', 'Male', 'Students', '8', '120', '35');
INSERT INTO `people` VALUES ('2', 'Qian Er', 'Female', 'Students', '9', '111', '31');
INSERT INTO `people` VALUES ('3', 'Sun San', 'Male', 'Students', '10', '123', '34');
INSERT INTO `people` VALUES ('4', 'Li Si', 'Female', 'Students', '11', '100', '30');
'''
db = DB('people')
 
# Increase
dict = {'name': 'Friday', 'sex': 'Male', 'job': 'Students', 'age': '8', 'height': '121', 'weight': '32'}
data = (dict)
print(data)
 
# Delete
# data = ('id=6').delete()
# print(data)
 
# Modify
# dict = {'age': '9', 'height': '121', 'weight': '31'}
# data = ('id=7').update(dict)
# print(data)
 
# query optimize where condition 'id<11'
# data = ('id,name,age,job').where([['id', '>', 1]]).order('id desc').limit('3').select()
# print(data)