Python自动化运维之异常处理

def testRaise(number):
    if number < 1:
        raise ValueError(‘Invalid value‘) #或者 raise ValueError,‘Invalid value‘
testRaise(0)

import os
try:
    openFile = open(‘notExistsFile.txt‘,‘r‘)
    fileContent = openFile.readlines()
except IOError:
    print(‘File not Exists‘
    if not os.path.exists(‘notExistsFile.txt‘):
        raise
except:
    print(‘process exception‘

格式：assert expression,‘information‘

def testAssert(x):
    assert x < 1,‘Invalid value‘
testAssert(1)
print(‘Valid value‘

AssertionError: Invaild value

try:
    可能触发异常的语句块
except [exceptionType]:
    捕获可能触发的异常[可以指定处理的异常类型]
except [exceptionType][,date]:
    捕获异常并获取附加数据
except:
    没有指定异常类型，捕获任意异常
else：
    没有触发异常时，执行的语句块

try:
    openFile = open(‘notExistsFile.txt‘,‘r‘)
    fileContent = openFile.readlines()
except IOError:   
    print(‘File not Exists‘)        # 执行
except: 
    print(‘process exception‘)      # 不执行
else:
    print(‘Reading the file‘)       # 不执行

In [157]: %run testError.py
File not Exists

try:
    try:
        openFile = open(‘notExistsFile.txt‘,‘r‘)
        fileContent = openFile.readlines()
    except IOError:
        print(‘File not Exists‘)      #执行
except:
    print(‘process exception‘)        #不执行 
else: 
    print(‘Reading the file‘)         #执行

In [159]: %run testError.py
File not Exists
Reading the file

try:
    语句块
except Exception:
    语句块

try:
    语句块
except (IOError,ValueError): 
    语句块

try:
    语句块
except: 
    语句块

import os
def write_test(fileName,content_iterable):
    try:
        pwd = open(fileName,‘w‘)
        for key,value in content_iterable.items():
            pwd.write(key+‘\t‘+value+‘\n‘)  #传入String类型参数同时加入换行符
    finally:
        pwd.close()
if __name__ == ‘__main__‘:
    fileName = ‘/usr/local/src/pyScript/fileOperation.txt‘
    dic = {‘name‘:‘Jmilk‘,‘age‘:‘23‘,‘city‘:‘BJ‘}
    if os.path.exists(fileName):
        write_test(fileName,dic)
    else:print(‘File not exist!‘)

In [3]: try:
   ...:     raise
   ...: except Exception:
   ...:     print(‘error‘)
   ...:     raise
   ...: finally:
   ...:     print(‘success‘)
   ...:
error
success
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-530db52949e7> in <module>()
      1 try:
----> 2     raise
      3 except Exception:
      4     print(‘error‘
      5     raise
TypeError: exceptions must be old-style classes or derived from BaseException, not NoneType

class testError(Exception):    #直接集成Exception类
    def __init__(self,arg):
        self.args = arg
try:
    raise testError(‘Just test‘)
except testError,info:
    print info.args

In [52]: %run test.py
(‘J‘, ‘u‘, ‘s‘, ‘t‘, ‘ ‘, ‘t‘, ‘e‘, ‘s‘, ‘t‘)

import os
def testWith(fileName):
    try:
        with open(fileName,‘r+‘) as pwd:
            pwd.readlines()
            print 2/0
    except Exception:
            print(‘File closed:‘,pwd.closed  #判断文件是否关闭
if __name__ == ‘__main__‘:
    if os.path.exists(‘/usr/local/src/pyScript/fileOperation.txt‘):
        testWith(‘/usr/local/src/pyScript/fileOperation.txt‘)
        print(‘continue‘)

In [17]: %run test.py
File closed: True    #没有call close()函数，文件仍然自动关闭。
continue

try:
    try:
        openFile = open(‘notExistsFile.txt‘,‘r‘)
        fileContent = openFile.readlines()
    except (IOError,ValueError) as info:  #或者except (IOError,ValueError)，info: 
        print info
except:
    print(‘process exception‘)
else:
    print(‘Reading the file‘)

In [164]: %run testError.py
[Errno 2] No such file or directory: ‘notExistsFile.txt‘

try:
    try:
        openFile = open(‘notExistsFile.txt‘,‘r‘)
        fileContent = openFile.readlines()
    except (IOError,ValueError),info:
        print dir(info)
        print info.args
except:
    print(‘process exception‘)
else:
    print(‘Reading the file‘)

In [44]: %run test.py
[‘__class__‘, ‘__delattr__‘, ‘__dict__‘, 
‘__doc__‘, ‘__format__‘, ‘__getattribute__‘, ‘__getitem__‘, 
‘__getslice__‘, ‘__hash__‘, ‘__init__‘, ‘__new__‘, ‘__reduce__‘, 
‘__reduce_ex__‘, ‘__repr__‘, ‘__setattr__‘, ‘__setstate__‘, 
‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘__unicode__‘, ‘args‘, 
‘errno‘, ‘filename‘, ‘message‘, ‘strerror‘]
(2, ‘No such file or directory‘)
Reading the file

tarceback.print_exc()函数。 
tarceback.print_exc()： 
print_exc(limit=None, file=None) 
Shorthand for ‘print_exception(sys.exc_type, sys.exc_value, sys.exc_traceback, limit, file)’. 
(In fact, it uses sys.exc_info() to retrieve the same information in a thread-safe way.)

import traceback
try:
    openFile = open(‘notExistsFile.txt‘,‘r‘)
    fileContent = openFile.readlines()
except IOError as info:
    print(‘File not Exists‘)
    print(info)
    traceback.print_exc()
    print(‘continue‘)
except:
    print(‘process exception‘)
else:
    print(‘Reading the file‘)

In [38]: %run test.py
File not Exists
[Errno 2] No such file or directory: ‘notExistsFile.txt‘
Traceback (most recent call last):
  File "/usr/local/src/pyScript/test.py", line 5, in <module>
    openFile = open(‘notExistsFile.txt‘,‘r‘)
IOError: [Errno 2] No such file or directory: ‘notExistsFile.txt‘
continue

import traceback
try:
    with open(‘notExistsFile.txt‘,‘r‘) as openFile:
        fileContent = openFile.readlines()
except IOError:
    with open(‘errorLog‘,‘w+‘) as errorInfo:
        traceback.print_exc(file=errorInfo)
    print(‘continue‘)
except:
    print(‘process exception‘)
else:
    print(‘Reading the file‘)

In [61]: %run test.py
continue
In [62]: cat errorLog
Traceback (most recent call last):
  File "/usr/local/src/pyScript/test.py", line 5, in <module>
    with open(‘notExistsFile.txt‘,‘r‘) as openFile:
IOError: [Errno 2] No such file or directory: ‘notExistsFile.txt‘

import sys  
try:  
    a=b  
    b=c  
except:  
    info=sys.exc_info()  
    print(info[0],":",info[1])

In [65]: %run test.py
<type ‘exceptions.NameError‘> : name ‘b‘ is not defined