Python標準異常開發(fā)經(jīng)驗總結(jié)

1、FileNotFoundError
嘗試打開文d:\openstack.txt文件由于文件不存在就會報出FIleNotFoundError：
f=open("d:\openstack.txt")
Traceback (most recent call last):
 File "<pyshell#0>", line 1, in <module>
 f=open("d:\openstack.txt")
FileNotFoundError: [Errno 2] No such file or directory: 'd:\openstack.txt'
 
2、ZeroDivisionError
除法運算或取模運算中，除數(shù)為零的情況
 >>> 5/0
Traceback (most recent call last):
 File "<pyshell#1>", line 1, in <module>
 5/0
ZeroDivisionError: division by zero
3、ImportError
一般是在導入模塊時，由于模塊不存在等原因?qū)е聢箦e
>>> import wwww
Traceback (most recent call last):
 File "<pyshell#2>", line 1, in <module>
 import wwww
ImportError: No module named 'wwww'
4、ValueError
 一般是由于傳入?yún)?shù)的數(shù)據(jù)類型錯誤引起報錯。
 >>> a="sterc"
>>> int(a)
Traceback (most recent call last):
 File "<pyshell#4>", line 1, in <module>
 int(a)
ValueError: invalid literal for int() with base 10: 'sterc'
>>>

try:
 You do your operations here
 ......................
except ExceptionI:
 If there is ExceptionI, then execute this block.
except ExceptionII:
 If there is ExceptionII, then execute this block.
 ......................
else:
 If there is no exception then execute this block. 
 
單個 try 語句可以有多個except語句。 當 try 塊包含可能拋出不同類型的異常聲明這是有用的
也可以提供一個通用的 except 子句來處理異常（不提倡）
except子句后，可以包括 else 子句。 如果代碼在try：塊不引發(fā)異常則代碼在 else 塊執(zhí)行
else是可以正常運行部存在異常的代碼，這不需要 try: 塊的保護
 try:
 fh = open("testfile", "w+")
 fh.write("This is my test file for exception handling!!")
except IOError:
 print ("Error: can't find file or read data")
else:
 print ("Written content in the file successfully")
 fh.close()
 
 正常執(zhí)行后就會生成testfile文件里面的內(nèi)容為：This is my test file for exception handling!
 而控制臺

try:
 fh = open("testfile", "r")
 fh.write("This is my test file for exception handling!!")
except (ValueError,ImportError,RuntimeError):
 print ("Error: can't find file or read data")
else:
 print ("Written content in the file successfully")
 fh.close()
 結(jié)果：
 Error: can't find file or read data #這里沒有報出是那個類型的標準錯誤。

try:
 You do your operations here;
 ......................
 Due to any exception, this may be skipped.

except ExceptionI:
 If there is ExceptionI, then execute this block.
except ExceptionII:
 If there is ExceptionII, then execute this block.

 This would always be executed.

try:
 fh = open("testfile", "r")
 fh.write("This is my test file for exception handling!!")
except (ValueError,ImportError,RuntimeError):
 print ("Error: can't find file or read data")
finally:
 print ("Written content in the file successfully")
 fh.close() #關(guān)閉文件
 結(jié)果：文件中沒有寫入內(nèi)容，
 控制臺

def functionName( level ):
 if level <1:
 raise Exception(level)
 # The code below to this would not be executed
 # if we raise the exception
 return level

try:
 Business Logic here...
except Exception as e:
 Exception handling here using e.args...
else:
 Rest of the code here...

#!/usr/bin/python3
def functionName( level ):
 if level <1:
 raise Exception(level)
 # The code below to this would not be executed
 # if we raise the exception
 return level
 
try:
 l=functionName(-10)
 print ("level=",l)
except Exception as e:
 print ("error in level argument",e.args[0])

class Networkerror(RuntimeError):
 def __init__(self, arg):
 self.args = arg

try:
 raise Networkerror("Bad hostname")
except Networkerror,e:
 print e.args