Inventory of URLError and HTTPError exception handling methods

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1. Introduction

This article mainly talks about URLError and HTTPError, as well as some processing methods.

2. URLError

1. Explain the three possible reasons for URLError:

 # 1. There is no network connection, that is, the machine cannot access the Internet. 
 
 # 2. Unable to connect to a specific server. 
 
 # 3. The server does not exist.

2. Case examples:

In the code, try-except statements are needed to surround and capture corresponding exceptions.

 # coding:UTF8 
 
 import urllib.request 
 
 request = urllib.request.urlopen( "http://www.baidu.com" ) 
 
 try:
    urllib.request.urlopen(request)
    print( "[Errno 11004] getaddrinfo failed" )
 except urllib.URLError as e:
 print(e.reason)

The urlopen method was used to access a non-existent URL.

Running results:

Note:

It shows that the error code is 11004 and the error reason is getaddrinfo failed.

HTTPError

HTTPError is a subclass of URLError. When a request is made using the urlopen method, the server will have a corresponding response object, which contains a digital "status code".

example:

The caught exception is HTTPError, which has a code attribute, which is the error code, and a reason attribute, which is an attribute of its parent class URLError.

 import urllib2
 req = urllib2.Request( 'http://blog.csdn.net/cqcre' )
 try:
 urllib2.urlopen(req)
 except urllib2.HTTPError, e:
 print e.code
 print e.reason

Running results:

1. Code analysis

The error code is 403 and the error reason is Forbidden, which means the server prohibits access.

As we know, the parent class of HTTPError is URLError. According to programming experience, the exception of the parent class should be written after the child class exception. If the child class cannot catch it, then the parent class exception can be caught.

2. Optimize the code

 import urllib2
 req = urllib2.Request( 'http://blog.csdn.net/cqcre' )
 try:
 urllib2.urlopen(req)
 except urllib2.HTTPError, e:
 print e.code
 except urllib2.URLError, e:
 print e.reason
 else :
 print "OK"    

If HTTPError is caught, the code is output and the URLError exception is not processed. If a non-HTTPError occurs, the URLError exception is caught and the cause of the error is output.

In addition, you can add the hasattr attribute to judge the attribute in advance. The code is rewritten as follows

 import urllib2
 req = urllib2.Request( 'http://blog.csdn.net/cqcre' )
 try:
 urllib2.urlopen(req)
 except urllib2.URLError, e:
 if hasattr(e, "code" ):
 print e.code
 if hasattr(e, "reason" ):
 print e.reason
 else :
 print "OK"    

3. Exception handling method

First, judge the abnormal attributes to avoid attribute output errors.

If the response is a "redirect", you need to locate another address to get the document, urllib2 will handle this.

Note:

When an HTTPError instance is generated, it will have a code attribute, which is the relevant error number sent by the server.

Because urllib2 can handle redirects, that is, codes starting with 3 can be processed, and numbers in the range of 100-299 indicate success, so only error numbers 400-599 are seen.

IV. Conclusion

This article is based on the basics, through case analysis and code display. It solves the problem of handling URLError null exceptions in practical applications. It introduces two main exception errors and provides solutions to the corresponding errors.

Everyone is welcome to try actively. Sometimes it is easy to implement something when you see others do it, but when you try to implement it yourself, there will always be various problems. Don't be too ambitious and be diligent in doing it, so that you can understand it more deeply.

The use of language can make readers understand the content of the article more clearly and intuitively. The code is very simple, I hope it will be helpful for learning.