詳解Flask開發(fā)技巧之異常處理

第詳解Flask開發(fā)技巧之異常處理目錄一、Flask內(nèi)置異常處理二、HTTPException類分析三、自定義異常處理類四、方便的定義自己的錯誤類五、注意事項

一、Flask內(nèi)置異常處理

要想在Flask中處理好異常，有一套自己的異常處理機制，首先，我們必須先知道Flask自己是如何處理異常的。去flask的源碼里找一找會發(fā)現(xiàn)，在flask源碼的app.py文件下，有很多會拋出異常的方法，其中拿一個舉例:

defhandle_exception(self,e):

"""Defaultexceptionhandlingthatkicksinwhenanexception

occursthatisnotcaught.Indebugmodetheexceptionwill

bere-raisedimmediately,otherwiseitisloggedandthehandler

fora500internalservererrorisused.Ifnosuchhandler

exists,adefault500internalservererrormessageisdisplayed.

..versionadded::0.3

exc_type,exc_value,tb=sys.exc_info()

got_request_exception.send(self,exception=e)

handler=self._find_error_handler(InternalServerError())

ifpagate_exceptions:

#ifwewanttorepropagatetheexception,wecanattemptto

#raiseitwiththewholetracebackincasewecandothat

#(thefunctionwasactuallycalledfromtheexceptpart)

#otherwise,wejustraisetheerroragain

ifexc_valueise:

reraise(exc_type,exc_value,tb)

else:

raisee

self.log_exception((exc_type,exc_value,tb))

ifhandlerisNone:

returnInternalServerError()

returnself.finalize_request(handler(e),from_error_handler=True)

我們發(fā)現(xiàn)在flask內(nèi)部對于500異常，會拋出這樣一個錯誤類InternalServerError()

classInternalServerError(HTTPException):

至此我們發(fā)現(xiàn)flask內(nèi)部異常通過繼承這個HTTPException類來處理，那么這個HTTPException類就是我們研究的重點。

二、HTTPException類分析

@implements_to_string

classHTTPException(Exception):

"""BaseclassforallHTTPexceptions.ThisexceptioncanbecalledasWSGI

applicationtorenderadefaulterrorpageoryoucancatchthesubclasses

ofitindependentlyandrendernicererrormessages.

code=None

description=None

def__init__(self,description=None,response=None):

super(HTTPException,self).__init__()

ifdescriptionisnotNone:

self.description=description

self.response=response

@classmethod

defwrap(cls,exception,name=None):

"""CreateanexceptionthatisasubclassofthecallingHTTP

exceptionandthe``exception``argument.

Thefirstargumenttotheclasswillbepassedtothe

wrapped``exception``,theresttotheHTTPexception.If

``e.args``isnotemptyand``e.show_exception``is``True``,

thewrappedexceptionmessageisaddedtotheHTTPerror

description.

..versionchanged::0.15.5

The``show_exception``attributecontrolswhetherthe

descriptionincludesthewrappedexceptionmessage.

..versionchanged::0.15.0

Thedescriptionincludesthewrappedexceptionmessage.

classnewcls(cls,exception):

_description=cls.description

show_exception=False

def__init__(self,arg=None,*args,**kwargs):

super(cls,self).__init__(*args,**kwargs)

ifargisNone:

exception.__init__(self)

else:

exception.__init__(self,arg)

@property

defdescription(self):

ifself.show_exception:

return"{}\n{}:{}".format(

self._description,exception.__name__,exception.__str__(self)

returnself._description

@description.setter

defdescription(self,value):

self._description=value

newcls.__module__=sys._getframe(1).f_globals.get("__name__")

name=nameorcls.__name__+exception.__name__

newcls.__name__=newcls.__qualname__=name

returnnewcls

@property

defname(self):

"""Thestatusname."""

from.httpimportHTTP_STATUS_CODES

returnHTTP_STATUS_CODES.get(self.code,"UnknownError")

defget_description(self,environ=None):

"""Getthedescription."""

returnu"p%s/p"%escape(self.description).replace("\n","br")

defget_body(self,environ=None):

"""GettheHTMLbody."""

returntext_type(

u'!DOCTYPEHTMLPUBLIC"-//W3C//DTDHTML3.2Final//EN"\n'

u"title%(code)s%(name)s/title\n"

u"h1%(name)s/h1\n"

u"%(description)s\n"

"code":self.code,

"name":escape(),

"description":self.get_description(environ),

defget_headers(self,environ=None):

"""Getalistofheaders."""

return[("Content-Type","text/html;charset=utf-8")]

defget_response(self,environ=None):

"""Getaresponseobject.Ifonewaspassedtotheexception

it'sreturneddirectly.

:paramenviron:theoptionalenvironfortherequest.This

canbeusedtomodifytheresponsedepending

onhowtherequestlookedlike.

:return:a:class:`Response`objectorasubclassthereof.

from.wrappers.responseimp