封装的Mysql简易操作

import pymysql
con=''
cur=''
def connect(host,user,passwd,db):
    global con
    global cur
    try:
        con=pymysql.connect(host=host,user=user,port=3306,passwd=passwd,db=db,charset="utf8")
        cur=con.cursor()
        return True
    except:
        print('Mysql数据库连接失败!')
        return False
def update(table,cname,cvalue,name,value,commit=True):
    global con
    sql='update '+table+' set '+name+"='"+value+"' where "+cname+"='"+cvalue+"'"
    try:
        query(sql)
        if commit==True:
            con.commit()
        return True
    except:
        return False
def create(table,value,main=False,commit=True):
    global con
    global cur
    sql='create table '+table +'('
    name=[]
    type=[]
    for n in value.keys():
        name.append(n)
    for n in value.values():
        type.append(n)
    i=0
    while i<len(value):
        if i ==len(value)-1:
            sql+=name[i]+' '+type[i].upper()
        else:
            sql+=name[i]+' '+type[i].upper()+','
        i+=1
    if main!=False:
        sql=sql+','+main+' INT NOT NULL AUTO_INCREMENT,PRIMARY KEY ( '+main+')'
    sql=sql+')' #ENGINE=InnoDB?DEFAULT?CHARSET=utf8
    try:
        query(sql)
        if commit==True:
            con.commit()
        return True
    except:
        return False
def insert(table,value,commit=True):
    global con
    sql='insert into '+table+'('
    i=0
    for n in value.keys():
        i=i+1
        if i!=len(value):
            sql=sql+n+','
        else:
            sql=sql+n+')values('
    i=0
    for n in value.values():
        i=i+1
        if i!=len(value):
            sql=sql+"'"+n+"'"+','
        else:
            sql=sql+"'"+n+"'"+')'
    try:
        query(sql)
        if commit==True:
            con.commit()
        return True
    except:
        return False
def select(table,name,vname,vvalue):
    global cur
    sql='select '+name+' from '+table+' where '+vname+"='"+vvalue+"'"
    try:
        query(sql)
    except:
        return None
    try:
        re=cur.fetchall()
        return str(re[0][0])
    except:
        return None
def query(sql):
    global cur
    return cur.execute(sql)
def delete(table,vname,vvalue,commit=True):
    global con
    sql='DELETE  FROM  '+table+' WHERE  '+vname+"='"+vvalue+"'"
    try:
        query(sql)
        if commit==True:
            con.commit()
        return True
    except:
        return False
def drop(table):
    sql='DROP TABLE  '+table
    try:
        query(sql)
        return True
    except:
        return False
def close():
    global con
    global cur
    cur.close()
    con.close()