Python Exception handling

Take a look at the code first:

Def calc (A, B):
    res = A/b
    return res

def main ():
    Money = input (' Enter how much: ')
    month = input (' Also several months: ')
    res = calc (int (money), Int (month))
    return res

Main ()

When you run the Money input 10,month enter 0 to see the results:

Run when money input Aa,month input HHH, view results: HHH

In the process of running, we need to process the exception, let the code continue to execute after the part, modify the code:

def main ():
    Money = input (' Enter how much: ')
    month = input (' Also several months: ')
    Try
        res = calc (int (money), Int (month))
    Except Zerodivisionerror as E: #try里面的代码出错, go except
        Print (' The number of months to repay cannot be 0 ', e)
    Print (' should also%s '% res per month)

Run, Money input 10,month enter 0 to view the results:

The reason for the error is that the code in the try is wrong and the except,res does not have a value at all, so let's change the code again:

def main ():
    Money = input (' Enter how much: ')
    month = input (' Also several months: ')
    Try
        res = calc (int (money), Int (month))
    Except Zerodivisionerror as E: #try里面的代码出错, go except
        Print (' The number of months to repay cannot be 0 ', e)
    Else
        Print (' should also%s '% res per month)

When we enter a letter, we still get an error, we can continue to modify the code:

def main ():
    Money = input (' Enter how much: ')
    month = input (' Also several months: ')
    Try
        res = calc (int (money), Int (month))
    Except Zerodivisionerror as E: #try里面的代码出错, go except
        Print (' The number of months to repay cannot be less than 1 ', e)
    Except ValueError as E:  #继续捕获其他异常
        Print (' input must be an integer. %s '%e)
    Else
        Print (' should also%s '%res per month)

There may be many unknown exceptions to the code, and we cannot predict that we can modify the code to catch all exceptions in order for the code to execute without terminating the error:

def main ():
    Money = input (' Enter how much: ')
    month = input (' Also several months: ')
    Try
        res = calc (int (money), Int (month))
    Except Zerodivisionerror as E: #try里面的代码出错, go except
        Print (' The number of months to repay cannot be less than 1 ', e)
    Except ValueError as E:  #继续捕获其他异常
        Print (' input must be an integer. %s '%e)
    Except Exception as E:  #捕捉全部异常
        Print (' Catch all exceptions%s '%e)
    Else
        Print (' should also%s '%res per month)

When we use try, we can also capture the complete error message, we need to introduce a new module Traceback, modify the code:

Import Traceback

def main ():
    Money = input (' Enter how much: ')
    month = input (' Also several months: ')
    Try
        res = calc (int (money), Int (month))
    Except Zerodivisionerror as E: #try里面的代码出错, go except
        Traceback.print_exc () #只是输出报错的详细信息, does not affect code run
        Print (' The number of months to repay cannot be less than 1 ', e)
    Except ValueError as E:  #继续捕获其他异常
        Print (' input must be an integer. %s '%e)
    Except Exception as E:  #捕捉全部异常
        Print (' Catch all exceptions%s '%e)
    Else
        Print (' should also%s '%res per month)

Execution Result:

================================== I'm a split line ==================================================

Import Pymysql
Def main2 ():
    Try
        conn = Pymysql.connect (host= ' 122.932.122.11 ', user= ' root ', password= ' 123456 ', db= ' test ')
    Except Exception as E:
        Print (' database not connected,%s '%e)
    Else
        cur = conn.cursor ()
        Except Exception as E:
        Print (' SQL statement has errors! %s SQL is "%s"% (e, SQL))
        Else
            res = Cur.fetchall ()
            return res
        #except和else不会同时走到, you can only walk the same, so you need to put the close cursor and the connection in two branches
        Finally:  #不管有没有捕捉到异常, will come here
            Cur.close ()
            Conn.close ()

================================== I'm a split line ==================================================

Import requests
def req ():
   r = Requests.get (' http://api.nnzhp.cn/api/user/all_stu ', headers={' Referer ': ' http://api.nnzhp.cn/'})
   If Len (R.json () [' Stu_info ']) <0:
      Pass
   Else
      Raise Exception (' Interface not data ') #主动抛出异常
Req ()

Python exception handling