# coding:utf-8import pymysqlclass Field(object):    passclass Expr(object):    def __init__(self, model, kwargs):        self.model = model        # How to deal with a non-dict parameter?        self.params = kwargs.values()        equations = [key + ‘ = %s‘ for key in kwargs.keys()]        self.where_expr = ‘where ‘ + ‘ and ‘.join(equations) if len(equations) > 0 else ‘‘    def update(self, **kwargs):        _keys = []        _params = []        for key, val in kwargs.iteritems():            if val is None or key not in self.model.fields:                continue            _keys.append(key)            _params.append(val)        _params.extend(self.params)        sql = ‘update %s set %s %s;‘ % (            self.model.db_table, ‘, ‘.join([key + ‘ = %s‘ for key in _keys]), self.where_expr)        return Database.execute(sql, _params)    def limit(self, rows, offset=None):        self.where_expr += ‘ limit %s%s‘ % (            ‘%s, ‘ % offset if offset is not None else ‘‘, rows)        return self    def select(self):        sql = ‘select %s from %s %s;‘ % (‘, ‘.join(self.model.fields.keys()), self.model.db_table, self.where_expr)        for row in Database.execute(sql, self.params).fetchall():            inst = self.model()            for idx, f in enumerate(row):                setattr(inst, self.model.fields.keys()[idx], f)            yield inst    def count(self):        sql = ‘select count(*) from %s %s;‘ % (self.model.db_table, self.where_expr)        (row_cnt, ) = Database.execute(sql, self.params).fetchone()        return row_cntclass MetaModel(type):    db_table = None    fields = {}    def __init__(cls, name, bases, attrs):        super(MetaModel, cls).__init__(name, bases, attrs)        fields = {}        for key, val in cls.__dict__.iteritems():            if isinstance(val, Field):                fields[key] = val        cls.fields = fields        cls.attrs = attrsclass Model(object):    __metaclass__ = MetaModel    def save(self):        insert = ‘insert ignore into %s(%s) values (%s);‘ % (            self.db_table, ‘, ‘.join(self.__dict__.keys()), ‘, ‘.join([‘%s‘] * len(self.__dict__)))        return Database.execute(insert, self.__dict__.values())    @classmethod    def where(cls, **kwargs):        return Expr(cls, kwargs)class Database(object):    autocommit = True    conn = None    db_config = {}    @classmethod    def connect(cls, **db_config):        cls.conn = pymysql.connect(host=db_config.get(‘host‘, ‘localhost‘), port=int(db_config.get(‘port‘, 3306)),                                   user=db_config.get(‘user‘, ‘root‘), passwd=db_config.get(‘password‘, ‘‘),                                   db=db_config.get(‘database‘, ‘test‘), charset=db_config.get(‘charset‘, ‘utf8‘))        cls.conn.autocommit(cls.autocommit)        cls.db_config.update(db_config)    @classmethod    def get_conn(cls):        if not cls.conn or not cls.conn.open:            cls.connect(**cls.db_config)        try:            cls.conn.ping()        except pymysql.OperationalError:            cls.connect(**cls.db_config)        return cls.conn    @classmethod    def execute(cls, *args):        cursor = cls.get_conn().cursor()        cursor.execute(*args)        return cursor    def __del__(self):        if self.conn and self.conn.open:            self.conn.close()def execute_raw_sql(sql, params=None):    return Database.execute(sql, params) if params else Database.execute(sql)