python每日一练

print("------test1------")
f = open("123.txt","r")          #用只读模式打开了一个不存在的文件
print("-----test2------")         #这句代码不会被执行

#运行结果：报错

------test1------
Traceback (most recent call last):
  File "D:\program\python\pythonyunxinwenjian\异常处理.py", line 3, in <module>
    f = open("123.txt","r")
FileNotFoundError: [Errno 2] No such file or directory: '123.txt'

#对比

try:
print("------test1------")
f = open("123.txt","r")
print("-----test2------")
except IOError:       #文件没找到，属于输入输出异常
    pass              #我自己在执行时，不知道哪里的错误，无法执行
                      #pass这句话的作用是，捕获到异常后跳过

#异常类型想要被捕获，需要一致

try:
    print(num)
    
#except IOError:
    #使用IOError运行程序时：
    
    Traceback(most
    recent
    call
    last):
    File
    "D:\program\python\pythonyunxinwenjian\异常处理.py", line
    26, in < module >
    print(num)
NameError: name
'num' is not defined


except NameError:
    #使用NameError运行程序时
    
    D:\program\python\python\python.exe
    D: / program / python / pythonyunxinwenjian / 异常处理.py
    有错误

    进程已结束, 退出代码0
    
    print("有错误")

#两种错误都有的异常处理

try:
    print("------test1------")
    f = open("123.txt","r")
    print("-----test2------")

    print(num)
except(NameError,IOError):  #将所有可能的错误全都包含进去
    print("有错误")

#获取错误描述

try:
  print("------test1------")
  f = open("123.txt","r")
  print("-----test2------")

  print(num)
except(NameError,IOError) as result:    #将所有可能的错误全都包含进去
  print("有错误")
  print(result)

#捕获所有的异常

try:
  print("------test1------")
  f = open("123.txt","r")
  print("-----test2------")

  print(num)
except Exception as result:    #Exception捕获所有的异常
  print("有错误")
  print(result)



#try   finally和嵌套
import time
try:
    f = open("test1.txt","r")
    try:
        while True:
            content = f.readline()
            if len(content) == 0:
                break
            time.sleep(2)
            print(content)
    finally:
        f.close()
        print("文件关闭")            #finally后面的操作一定会执行
except Exception as result:
    print("发生异常")
    print(result)


f = open("gushi.txt","w")
f.write("窗前明月光，疑是地上霜,举头望明月，低头尿裤裆")
f.close()

f = open("gushi.txt","r")
content = f.readlines()
print(content)