I'm still relatively new to Python, so if this is an obvious question, I apologize.
My question is in regard to the urllib2 library, and it's urlopen function. Currently I'm using this to load a large amount of pages from another server (they are all on the same remote host) but the script is killed every now and then by a timeout error (I assume this is from the large requests).
Is there a way to keep the script running after a timeout? I'd like to be able to fetch all of the pages, so I want a script that will keep trying until it gets a page, and then moves on.
On a side note, would keeping the connection open to the server help?
Next time the error occurs, take note of the error message. The last line will tell you the type of exception. For example, it might be a urllib2.HTTPError. Once you know the type of exception raised, you can catch it in a try...except block. For example:
import urllib2
import time
for url in urls:
while True:
try:
sock=urllib2.urlopen(url)
except (urllib2.HTTPError, urllib2.URLError) as err:
# You may want to count how many times you reach here and
# do something smarter if you fail too many times.
# If a site is down, pestering it every 10 seconds may not
# be very fruitful or polite.
time.sleep(10)
else:
# Success
contents=sock.read()
# process contents
break # break out of the while loop
The missing manual of urllib2 might help you
Related
I have a program and in order verify that the user doesnt download such big files using input i need a time limit on how long each request is allowed to take.
Does anyone know a good way to put a time limit(/lifetime) on each python requests get requests so if it takes 10 seconds an exception will be thrown.
Thanks
You can define your own timeout like:
requests.get('https://github.com/', timeout=0.001)
You can pass an additional timeout parameter to every request you make. This is always recommended as it will make your code more robust to hanging indefinitely in case you don't receive a response from the other end.
requests.get('https://github.com/', timeout=0.001)
Read the official python request documentation for timeouts here.
Disclaimer: This is similar to some other questions relating to this error but my program is not using any multi-threading/processing and I'm working with the 'requests' module instead of raw socket commands so none of the solutions I saw related to my issue.
I have a basic status-checking program running Python 3.4 on Windows that uses a GET request to pull some data off a status site hosted by a number of servers I have to keep watch over. The core code is setup like this:
import requests
import time
URL_LIST = [some, list, of, the, status, sites] # https:// sites
session = requests.session()
previous_data = ""
while 1:
data = ""
for url in URL_LIST:
headers = {'X-Auth-Token': Associated_Auth_Token}
try:
status = session.get(url, headers=headers).json()['status']
except ConnectionError:
status = "SERVER DOWN"
data += "%s \t%s\n" % (url, status)
if data != previous_data:
print(data)
previous_data = data
time.sleep(15)
...which typically runs just fine for hours (this script is intended to run 24/7 and has additional logging built in I left out here for simplicity and relevance) but eventually it crashes and throws the error mentioned in the title:
[WinError 10048] Only one usage of each socket address (protocol/network address/port) is normally permitted
The servers I'm requesting from are notoriously slow at times (and sometimes go down entirely, hence the try/except) so my inclination would be that after looping this over and over eventually a request has not fully finished before the next request comes through and Windows tries to step on itself, but I don't see how that could happen with my code since it iterates serially through the URLs.
Also, if this is a TIME_WAIT issue as some other related posts ran into, I'd rather not have to wait for that to finish since I'd like to update every 15 seconds or better, so then I considered closing and opening a new requests session every so often since it typically works fine for hours before hitting a snag, but based off Lukasa's comment here:
To avoid getting sockets in TIME_WAIT, the best thing to do is to use a single Session object at as high a scope as you can and leave it open for the lifetime of your program. Requests will do its best to re-use the sockets as much as possible, which should prevent them lapsing into TIME_WAIT
...it sounds that is not a good idea - though when he says 'lifetime of your program' he may not intend the statement to include 24/7 use as in my case.
So instead of blindly trying things and waiting some number of hours for the program to crash again so I can see if the error changes, I wanted to consult the wealth of knowledge here first to see if anyone can see what's going wrong and knows how I should fix it.
Thanks!
import requests
while True:
try:
posting = requests.post(url,json = data,headers,timeout = 3.05)
except requests.exceptions.ConnectionError as e:
continue
# If a read_timeout error occurs, start from the beginning of the loop
except requests.exceptions.ReadTimeout as e:
continue
a link to more code : Multiple accidental POST requests in Python
This code is using requests library to perform POST requests indefinitely. I noticed that when try fails multiple of times and the while loop starts all over multiple of times, that when I can finally send the post request, I find out multiple of entries from the server side at the same second. I was writing to a txt file at the same time and it showed one entry only. Each entry is 5 readings. Is this an issue with the library itself? Is there a way to fix this?! No matter what kind of conditions that I put it still doesn't work :/ !
You can notice the reading at 12:11:13 has 6 parameters per second while at 12:14:30 (after the delay, it should be every 10 seconds) it is a few entries at the same second!!! 3 entries that make up 18 readings in one second, instead of 6 only!
It looks like the server receives your requests and acts upon them but fails to respond in time (3s is a pretty low timeout, a load spike/paging operation can easily make the server miss it unless it employs special measures). I'd suggest to
process requests asynchronously (e.g. spawn threads; Asynchronous Requests with Python requests discusses ways to do this with requests) and do not use timeouts (TCP has its own timeouts, let it fail instead).
reuse the connection(s) (TCP has quite a bit of overhead for connection establishing/breaking) or use UDP instead.
include some "hints" (IDs, timestamps etc.) to prevent the server from adding duplicate records. (I'd call this one a workaround as the real problem is you're not making sure if your request was processed.)
From the server side, you may want to:
Respond ASAP and act upon the info later. Do not let pending action prevent answering further requests.
I am using urlib library in python,
For any error in URL ,I am using try catch block to catch it.
But sometimes I am getting empty data in url, how to check or validate the empty data from URL .And also using the timeout , given 25 seconds.is it good to give 25 seconds or it should be below 10?
You can use whatever timeout length is appropriate for your program. If you expect that it might sometimes take whatever URL you're querying up to 25 seconds to respond, then 25 is appropriate. If it should never take more than a few seconds to respond, and you can safely assume that if it's taken longer than a few seconds the URL must be dead, then you can lower the timeout. In general I think it's a good idea to be conservative with timeouts. It's better to make the error case a little slower with a timeout that's too long, rather than falsely triggering an error with a timeout that's too short.
You can check for an empty response from urllib2 by doing something like this
fh = urllib2.urlopen(url)
response = fh.read()
if not response:
# Do whatever error handling you want. You don't necessarily need to raise Exception.
raise Exception("Empty response")
Is that what you're looking for?
I writing app that connect to a web server (I am the owner of he server) sends information provided by the user, process that information and send result back to the application. The time needed to process the results depends on the user request (from few seconds to a few minutes).
I use a infinite loop to check if the file exist (may be there is a more intelligent approach... may be I could estimated the maximum time a request could take and avoid using and infinite loop)
the important part of the code looks like this
import time
import mechanize
br = mechanize.Browser()
br.set_handle_refresh(False)
proxy_values={'http':'proxy:1234'}
br.set_proxies(proxy_values)
While True:
try:
result=br.open('http://www.example.com/sample.txt').read()
break
except:
pass
time.sleep(10)
Behind a proxy the loop never ends, but if i change the code for something like this,
time.sleep(200)
result=br.open('http://www.example.com/sample.txt').read()
i.e. I wait enough time to ensure that the file is created before trying to read it, I indeed get the file :-)
It seems like if mechanize ask for a file that does not exits everytime mechanize will ask again I will get no file...
I replicated the same behavior using Firefox. I ask for a non-existing file then I create that file (remember I am the owner of the server...) I can not get the file.
And using mechanize and Firefox I can get deleted files...
I think the problem is related to the Proxy cache, I think I can´t delete that cache, but may be there is some way to tell the proxy I need to recheck if the file exists...
Any other suggestion to fix this problem?
The simplest solution could be to add a (unused) GET parameter to avoid caching the request.
ie:
i = 0
While True:
try:
result=br.open('http://www.example.com/sample.txt?r=%d' % i).read()
break
except:
i += 1
time.sleep(10)
The extra parameter should be ignored by the web application.
A HTTP HEAD is probably the correct way to do this, see this question for a example.