python script library error while continuously executing script - python-2.7

Question

Error while running python script to get pixel points from google static map image. I got the python script from Google maps - how to get building's polygon coordinates from address?
I use python2.7 to execute the script
Initially when i was running the script i was not getting any error, but after continuous running for 3-4 hours i am getting the following error
Traceback (most recent call last):
File "pyscript.py", line 19, in <module>
imgBuildings = io.imread(urlBuildings)
File "/usr/local/lib/python2.7/dist-packages/skimage/io/_io.py", line 60, in i
with file_or_url_context(fname) as fname:
File "/usr/lib/python2.7/contextlib.py", line 17, in __enter__
return self.gen.next()
File "/usr/local/lib/python2.7/dist-packages/skimage/io/util.py", line 29, in
u = urlopen(resource_name)
File "/usr/lib/python2.7/urllib2.py", line 154, in urlopen
return opener.open(url, data, timeout)
File "/usr/lib/python2.7/urllib2.py", line 435, in open
response = meth(req, response)
File "/usr/lib/python2.7/urllib2.py", line 548, in http_response
'http', request, response, code, msg, hdrs)
File "/usr/lib/python2.7/urllib2.py", line 473, in error
return self._call_chain(*args)
File "/usr/lib/python2.7/urllib2.py", line 407, in _call_chain
result = func(*args)
File "/usr/lib/python2.7/urllib2.py", line 556, in http_error_default
raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
urllib2.HTTPError: HTTP Error 403: Forbidden
AS i am new to python i am not sure how to fix it ? Is this some kind of cache issue?
Help very much appreciated.

Answer 1

I've seen this problem quite a lot and its due to intermittent network drop errors. There is a recursive trick with try/catch exception handling that will avoid this ever happening, even if your network goes down for hours.
To explain: You attempt a download. If it fails, the download will attempt a recursive retry again 1/4,1/2,1,2,4,8,... seconds later, waiting up to 1 hour to get the next download. If you are working in a company for instance, the network might go down over the weekend, but your code will just poll for 1 hour (maximum) and then recover again when the network is fixed.
import time
def recursiveBuildingGetter( urlBuildings, waitTime=0.25 ):
try:
imgBuildings = io.imread(urlBuildings)
except:
print "Warning: Failure at time %f secs for %s" % ( waitTime, str(urlBuildings) )
waitTime = waitTime * 2.0
if ( waitTime > 3600.0 ):
waitTime = 3600.0
time.sleep(waitTime)
imgBuildings = recursiveBuildingGetter( urlBuilding, waitTime )
if ( waitTime == 3600.0 ):
waitTime = 0.25
return imgBuildings