【再回首Python之美】【異常處理】try-except
阿新 • • 發佈：2019-02-12
使用方法直接跳看：推薦使用的異常處理流程；推薦的內建函式的封裝函式
異常處理必要性
為了保證程式的健壯性，將可能出現異常退出的程式碼用try……except來處理
捕獲異常的各種方法
1.捕獲所有異常
print "\r\n=======try-except========="
try:
open('unexistFile')
except:
print "failed to open."2.捕獲特殊異常，如ctrl+c等
KeyboardInterrupt和SystemExit，是與Exception平級的異常。
print '\r\n======try-except (KeyboardInterupt, SystemExit)======' try: while 1: pass except (KeyboardInterrupt, SystemExit):#ctrl+c等導致app退出異常 print 'app will exit, handle app exitence.'
3.捕獲具體異常，1/0等
print "\r\n======try-except ZeroDivisionError,e======="
try:
1/0 #除數為零
except ZeroDivisionError, e:
print 'ZeroDivisionError:',e4.捕獲多個具體的異常
#try-except (E1, E2，……En)[,e]:捕獲多個異常 print '\r\n======try-except (E1, E2，……En)[,e]======' try: 1/0 except (NameError,ZeroDivisionError),e: print repr(e)
5.待追加
簡單示例程式碼
編譯執行#ex_except.py def dumpFile_withExcept(path): try: f = file(path) print 'Succeed open file' f.close() except: print 'Failed open file, file not exists.' return False return True def dumpFile_nonExcept(path): f = file(path) f.close() #test dumpFile_withExcept('non-exist.txt') dumpFile_nonExcept('non-exist.txt')
可知
有了try……excepty異常捕捉處理的dumpFile_withExcept函式開啟不存在檔案時，try丟擲異常，然後由except捕獲並執行except程式碼塊。
沒有異常捕捉處理的dumpFile_nonExcept函式開啟不存在檔案時，由程式直接退出並給出IOError等資訊。
示例程式碼（追加）
#ex_try-except.py
self_file = __file__
#try-except，捕獲所有異常
print "\r\n=======try-except========="
try:
open('unexistFile')
except:
print "failed to open."
#try-except + trceback，列印異常堆疊以及錯誤資訊
print "\r\n=======traceback + try-except========="
import traceback #use traceback module
try:
open('unexistFile')
except:
print 'traceback.print_exc():',traceback.print_exc()
print 'traceback.format_exc():\n%s' % traceback.format_exc()
#try-except Exception,e，捕獲所有異常
print '\r\n======try-except Exception,e======'
try:
open('unexistFile')
except Exception,e:
print 'ErrorInfo:',e
print 'ErrorInfo:',e.message
print 'ErrorInfo:',str(e)
print "ErrorInfo:",repr(e)
#try-except Exception,(errCode, errMsg)，捕獲所有異常以及具體錯誤碼
print '\r\n======try-except Exception,(errCode, errMsg)======'
import errno #use errno module
try:
open('unexistFile')
except Exception,(errCode,errMsg):
if errCode == errno.ENOENT:
print 'failed to open, no such file.'
elif errCode == errno.EPERM:
print 'failed to open, permission denied'
else:
print errMsg
#try-except ErrorType, e，捕獲具體異常
print '\r\n======try-except (KeyboardInterupt, SystemExit)======'
try:
while 1:
pass
except (KeyboardInterrupt, SystemExit):#ctrl+c等導致app退出異常
print 'app will exit, handle app exitence.'
print "\r\n======try-except NameError,e======="
try:
print unexistVal #訪問一個未申明的變數
except NameError, e:
print repr(e)
print "\r\n======try-except ZeroDivisionError,e======="
try:
1/0 #除數為零
except ZeroDivisionError, e:
print 'ZeroDivisionError:',e
print "\r\n======try-except IndexError,e======="
try:
lst = []
print lst[99] #請求的索引超出序列範圍
except IndexError,e:
print 'IndexError:',e.message
print "\r\n======try-except KeyError,e======="
try:
adct = {'Tom':25, 'John':18, 'Ann':20}
print adct['Kitty'] #請求一個不存在的字典關鍵字
except KeyError,e:
print 'KeyError:',e
print "\r\n======try-except IOError,e======="
try:
f = open('unexistFile') #開啟一個不存在的檔案或目錄
except IOError,e:
print 'IOError:',e
print "\r\n======try-except AttributeError,e======="
try:
class Car(object):
pass
car = Car()
print car.color #訪問未知的物件屬性
except AttributeError, e:
print 'AttributeError:',e
#try-except-……-except，捕獲具體異常並具體處理
print '\r\n=====try-except-……-except=========='
try:
1/0
except NameError, e:
print 'NameError:',e
except ZeroDivisionError, e: #由此except抓獲1/0丟擲的異常
print 'ZeroDivisionError:',e
except IndexError,e:
print 'IndexError:',e
except KeyError,e:
print 'KeyError:',e
except IOError,e:
print 'IOError:',e
except AttributeError, e:
print 'AttributeError:',e
except:#預設except必須作為最後一個except
print 'Unknown Error:',errno
#(start)推薦使用的異常處理流程
print '\r\n=====try-except======'
import errno #use errno module
import traceback #use traceback module
def handleException(errCode, errMsg):
if errCode == errno.ENOENT:
print 'failed to open, no such file.'
elif errCode == errno.EPERM:
print 'failed to open, permission denied'
else:
print errMsg
try:
open('unexistFile')
except Exception,(errCode,errMsg):
print traceback.format_exc()
handleException(errCode, errMsg)
#(end)推薦使用的異常處理流程
#(start)推薦的內建函式的封裝函式
print '\r\n======define safe function====='
import errno #use errno module
import traceback #use traceback module
def safe_open(file_path, mode):
try:
ret = open(file_path, mode)
except Exception,(errCode, errMsg):
print traceback.format_exc()
if errCode == errno.ENOENT:
ret = 'ErrorInfo:failed to open, no such file.'
elif errCode == errno.EPERM:
ret = 'ErrorInfo:failed to open, permission denied.'
else:
ret = errMsg
return ret
f = safe_open('unexistFile', 'r')
#(end)推薦的內建函式的封裝函式
print '\r\nexit %s' % self_file執行結果：
>>>
=================== RESTART: C:\Python27\ex_try-except.py ===================
=======try-except=========
failed to open.
=======traceback + try-except=========
traceback.print_exc():Traceback (most recent call last):
File "C:\Python27\ex_try-except.py", line 16, in <module>
open('unexistFile')
IOError: [Errno 2] No such file or directory: 'unexistFile'
None
traceback.format_exc():
Traceback (most recent call last):
File "C:\Python27\ex_try-except.py", line 16, in <module>
open('unexistFile')
IOError: [Errno 2] No such file or directory: 'unexistFile'
======try-except Exception,e======
ErrorInfo: [Errno 2] No such file or directory: 'unexistFile'
ErrorInfo:
ErrorInfo: [Errno 2] No such file or directory: 'unexistFile'
ErrorInfo: IOError(2, 'No such file or directory')
======try-except Exception,(errCode, errMsg)======
failed to open, no such file.
======try-except (KeyboardInterupt, SystemExit)======
app will exit, handle app exitence.
======try-except NameError,e=======
NameError("name 'unexistVal' is not defined",)
======try-except ZeroDivisionError,e=======
ZeroDivisionError: integer division or modulo by zero
======try-except IndexError,e=======
IndexError: list index out of range
======try-except KeyError,e=======
KeyError: 'Kitty'
======try-except IOError,e=======
IOError: [Errno 2] No such file or directory: 'unexistFile'
======try-except AttributeError,e=======
AttributeError: 'Car' object has no attribute 'color'
=====try-except-……-except==========
ZeroDivisionError: integer division or modulo by zero
=====try-except======
Traceback (most recent call last):
File "C:\Python27\ex_try-except.py", line 132, in <module>
open('unexistFile')
IOError: [Errno 2] No such file or directory: 'unexistFile'
failed to open, no such file.
======define safe function=====
Traceback (most recent call last):
File "C:\Python27\ex_try-except.py", line 146, in safe_open
ret = open(file_path, mode)
IOError: [Errno 2] No such file or directory: 'unexistFile'
exit C:\Python27\ex_try-except.py
>>>
(end)