初学 python 之 模拟sql语句实现对员工表格的增删改查

具体需求:

员工信息表程序，实现增删改查操作：

可进行模糊查询，语法支持下面3种:

　　select name,age from staff_data where age > 22                  多个查询参数name,age 用','分割

　　select * from staff_data where dept = 人事

　　select * from staff_data where enroll_date like 2013

查到的信息，打印后，最后面还要显示查到的条数

可创建新员工纪录，以phone做唯一键，phone存在即提示,staff_id需自增,添加多个记录record1/record2中间用'/'分割

　　insert into staff_data values record1/record2

可删除指定员工信息纪录，输入员工id，即可删除

　　delete from staff_data where staff_id>=5andstaff_id<=10

可修改员工信息，语法如下:

　　update staff_table set dept=Market,phone=13566677787  where dept = 运维   多个set值用','分割

 

使用re模块,os模块,充分使用函数精简代码,熟练使用 str.split()来解析格式化字符串

由于,sql命令中的几个关键字符串有一定规律,只出现一次,并且有顺序!!!

按照key_lis = ['select', 'insert', 'delete', 'update', 'from', 'into', 'set', 'values', 'where', 'limit']的元素顺序分割sql.  

分割元素作为sql_dic字典的key放进字典中.分割后的列表为b,如果len(b)>1,说明sql字符串中含有分割元素,同时b[0]对应上一个分割元素的值,b[-1]为下一次分割对象!

这样不断迭代直到把sql按出现的所有分割元素分割完毕,但注意这里每次循环都是先分割后赋值!!!当前分割元素比如'select'对应的值,需要等到下一个分割元素

比如'from'执行分割后的列表b,其中b[0]的值才会赋值给sql_dic['select'],所以最后一个分割元素的值,不能通过上述循环来完成,必须先处理可能是最后一个分割元素,再正常循环!!

在这sql语句中,有可能成为最后一个分割元素的 'limit' ,'values', 'where',  按优先级别,先处理'limit' ,再处理'values'或 'where'.....

处理完得到sql_dic后,就是你按不同命令执行,对数据文件的增删改查,最后返回处理结果!!

 

# _*_coding:utf-8_*_
# Author:Jaye He
import re
import os


def sql_parse(sql, key_lis):
    '''
    解析sql命令字符串,按照key_lis列表里的元素分割sql得到字典形式的命令sql_dic
    :param sql:
    :param key_lis:
    :return:
    '''
    sql_list = []
    sql_dic = {}
    for i in key_lis:
        b = [j.strip() for j in sql.split(i)]
        if len(b) > 1:
            if len(sql.split('limit')) > 1:
                sql_dic['limit'] = sql.split('limit')[-1]
            if i == 'where' or i == 'values':
                sql_dic[i] = b[-1]
            if sql_list:
                sql_dic[sql_list[-1]] = b[0]
            sql_list.append(i)
            sql = b[-1]
        else:
            sql = b[0]
        if sql_dic.get('select'):
            if not sql_dic.get('from') and not sql_dic.get('where'):
                sql_dic['from'] = b[-1]
    if sql_dic.get('select'):
        sql_dic['select'] = sql_dic.get('select').split(',')
    if sql_dic.get('where'):
        sql_dic['where'] = where_parse(sql_dic.get('where'))
    return sql_dic


def where_parse(where):
    '''
    格式化where字符串为列表where_list,用'and', 'or', 'not'分割字符串
    :param where:
    :return:
    '''
    casual_l = [where]
    logic_key = ['and', 'or', 'not']
    for j in logic_key:
        for i in casual_l:
            if i not in logic_key:
                if len(i.split(j)) > 1:
                    ele = i.split(j)
                    index = casual_l.index(i)
                    casual_l.pop(index)
                    casual_l.insert(index, ele[0])
                    casual_l.insert(index+1, j)
                    casual_l.insert(index+2, ele[1])
                    casual_l = [k for k in casual_l if k]
    where_list = three_parse(casual_l, logic_key)
    return where_list


def three_parse(casual_l, logic_key):
    '''
    处理临时列表casual_l中具体的条件,'staff_id>5'-->['staff_id','>','5']
    :param casual_l:
    :param logic_key:
    :return:
    '''
    where_list = []
    for i in casual_l:
        if i not in logic_key:
            b = i.split('like')
            if len(b) > 1:
                b.insert(1, 'like')
                where_list.append(b)
            else:
                key = ['<', '=', '>']
                new_lis = []
                opt = ''
                lis = [j for j in re.split('([=<>])', i) if j]
                for k in lis:
                    if k in key:
                        opt += k
                    else:
                        new_lis.append(k)
                new_lis.insert(1, opt)
                where_list.append(new_lis)
        else:
            where_list.append(i)
    return where_list


def sql_action(sql_dic, title):
    '''
    把解析好的sql_dic分发给相应函数执行处理
    :param sql_dic:
    :param title:
    :return:
    '''
    key = {'select': select,
           'insert': insert,
           'delete': delete,
           'update': update}
    res = []
    for i in sql_dic:
        if i in key:
            res = key[i](sql_dic, title)
    return res


def select(sql_dic, title):
    '''
    处理select语句命令
    :param sql_dic:
    :param title:
    :return:
    '''
    with open('staff_data', 'r', encoding='utf-8') as fh:
        filter_res = where_action(fh, sql_dic.get('where'), title)
        limit_res = limit_action(filter_res, sql_dic.get('limit'))
        search_res = search_action(limit_res, sql_dic.get('select'), title)
    return search_res


def insert(sql_dic, title):
    '''
    处理insert语句命令
    :param sql_dic:
    :param title:
    :return:
    '''
    with open('staff_data', 'r+', encoding='utf-8') as f:
        data = f.readlines()
        phone_list = [i.strip().split(',')[4] for i in data]
        ins_count = 0
        if not data:
            new_id = 1
        else:
            last = data[-1]
            last_id = int(last.split(',')[0])
            new_id = last_id+1
        record = sql_dic.get('values').split('/')
        for i in record:
            if i.split(',')[3] in phone_list:
                print('\033[1;31m%s 手机号已存在\033[0m' % i)
            else:
                new_record = '%s,%s\n' % (str(new_id), i)
                f.write(new_record)
                new_id += 1
                ins_count += 1
        f.flush()
    return ['insert successful'], [str(ins_count)]


def delete(sql_dic, title):
    '''
    处理delete语句命令
    :param sql_dic:
    :param title:
    :return:
    '''
    with open('staff_data', 'r', encoding='utf-8') as r_file,\
            open('staff_data_bak', 'w', encoding='utf-8') as w_file:
        del_count = 0
        for line in r_file:
            dic = dict(zip(title.split(','), line.split(',')))
            filter_res = logic_action(dic, sql_dic.get('where'))
            if not filter_res:
                w_file.write(line)
            else:
                del_count += 1
        w_file.flush()
    os.remove('staff_data')
    os.rename('staff_data_bak', 'staff_data')
    return ['delete successful'], [str(del_count)]


def update(sql_dic, title):
    '''
    处理update语句命令
    :param sql_dic:
    :param title:
    :return:
    '''
    set_l = sql_dic.get('set').strip().split(',')
    set_list = [i.split('=') for i in set_l]
    update_count = 0
    with open('staff_data', 'r', encoding='utf-8') as r_file,\
            open('staff_data_bak', 'w', encoding='utf-8') as w_file:
        for line in r_file:
            dic = dict(zip(title.split(','), line.strip().split(',')))
            filter_res = logic_action(dic, sql_dic.get('where'))
            if filter_res:
                for i in set_list:
                    k = i[0]
                    v = i[-1]
                    dic[k] = v
                line = [dic[i] for i in title.split(',')]
                update_count += 1
                line = ','.join(line)+'\n'
            w_file.write(line)
        w_file.flush()
    os.remove('staff_data')
    os.rename('staff_data_bak', 'staff_data')
    return ['update successful'], [str(update_count)]


def where_action(fh, where_list, title):
    '''
    具体处理where_list里的所有条件
    :param fh:
    :param where_list:
    :param title:
    :return:
    '''
    res = []
    if len(where_list) != 0:
        for line in fh:
            dic = dict(zip(title.split(','), line.strip().split(',')))
            if dic['name'] != 'name':
                logic_res = logic_action(dic, where_list)
                if logic_res:
                    res.append(line.strip().split(','))
    else:
        res = [i.split(',') for i in fh.readlines()]
    return res
    pass


def logic_action(dic, where_list):
    '''
    判断数据文件中每一条是否符合where_list条件
    :param dic:
    :param where_list:
    :return:
    '''
    logic = []
    for exp in where_list:
        if type(exp) is list:
            exp_k, opt, exp_v = exp
            if exp[1] == '=':
                opt = '=='
            logical_char = "'%s'%s'%s'" % (dic[exp_k], opt, exp_v)
            if opt != 'like':
                exp = str(eval(logical_char))
            else:
                if exp_v in dic[exp_k]:
                    exp = 'True'
                else:
                    exp = 'False'
        logic.append(exp)
    res = eval(' '.join(logic))
    return res


def limit_action(filter_res, limit_l):
    '''
    用列表切分处理显示符合条件的数量
    :param filter_res:
    :param limit_l:
    :return:
    '''
    if limit_l:
        index = int(limit_l[0])
        res = filter_res[:index]
    else:
        res = filter_res
    return res


def search_action(limit_res, select_list, title):
    '''
    处理需要查询并显示的title和相应数据
    :param limit_res:
    :param select_list:
    :param title:
    :return:
    '''
    res = []
    fields_list = title.split(',')
    if select_list[0] == '*':
        res = limit_res
    else:
        fields_list = select_list
        for data in limit_res:
            dic = dict(zip(title.split(','), data))
            r_l = []
            for i in fields_list:
                r_l.append((dic[i].strip()))
            res.append(r_l)
    return fields_list, res


if __name__ == '__main__':
    with open('staff_data', 'r', encoding='utf-8') as f:
        title = f.readline().strip()
    key_lis = ['select', 'insert', 'delete', 'update', 'from', 'into', 'set', 'values', 'where', 'limit']
    while True:
        sql = input('请输入sql命令,退出请输入exit:').strip()
        sql = re.sub(' ', '', sql)
        if len(sql) == 0:continue
        if sql == 'exit':break
        sql_dict = sql_parse(sql, key_lis)
        fields_list, fields_data = sql_action(sql_dict, title)
        print('\033[1;33m结果如下:\033[0m')
        print('-'.join(fields_list))
        for data in fields_data:
            print('-'.join(data))