Python: Socket.timeout not handled by except

Question

Some times I can effectively handle the socket.timeout, although some other times I get that socket timeout error and my script stops abruptly... Is there something I'm missing in my exception handling? how come it goes right trough it?

Happens randomly in either one of the following pieces of code:

First snippet:

for _ in range(max_retries):
    try:
        req = Request(url, headers={'User-Agent' :'Mozilla/5.0'})
        response = urlopen(req,timeout=5)
        break
    except error.URLError as err: 
        print("URL that generated the error code: ", url)
        print("Error description:",err.reason)
    except error.HTTPError as err:
        print("URL that generated the error code: ", url)
        print("Error code:", err.code)
        print("Error description:", err.reason)
    except socket.timeout:
        print("URL that generated the error code: ", url)
        print("Error description: No response.")
    except socket.error:
        print("URL that generated the error code: ", url)
        print("Error description: Socket error.")

if response.getheader('Content-Type').startswith('text/html'):
    htmlBytes = response.read()
    htmlString = htmlBytes.decode("utf-8")
    self.feed(htmlString)

Second snippet

for _ in range(max_retries):
    try:
        req = Request(i, headers={'User-Agent' :'Mozilla/5.0'})
        with urlopen(req,timeout=5) as response, open(aux, 'wb') as out_file:
            shutil.copyfileobj(response, out_file)  
        with open(path, fname), 'a') as f:
            f.write(("link" + str(intaux) + "-" + auxstr + str(index) + i[-4:] + " --- " + metadata[index%batch] + '\n'))
        break
    except error.URLError as err:
        print("URL that generated the error code: ", i)
        print("Error description:",err.reason)
    except error.HTTPError as err:
        print("URL that generated the error code: ", i)
        print("Error code:", err.code)
        print("Error description:", err.reason)
    except socket.timeout:
        print("URL that generated the error code: ", i)
        print("Error description: No response.")
    except socket.error:
        print("URL that generated the error code: ", i)
        print("Error description: Socket error.")

The error:

Traceback (most recent call last):
  File "/mydir/crawler.py", line 202, in <module>
    spider("urls.txt", maxPages=0, debug=1, dailyRequests=9600) 
  File "/mydir/crawler.py", line 142, in spider
    parser.getLinks(url + "?start=" + str(currbot) + "&tab=" + auxstr,auxstr)
  File "/mydir/crawler.py", line 81, in getLinks
    htmlBytes = response.read()
  File "/usr/lib/python3.5/http/client.py", line 455, in read
    return self._readall_chunked()
  File "/usr/lib/python3.5/http/client.py", line 561, in _readall_chunked
    value.append(self._safe_read(chunk_left))
  File "/usr/lib/python3.5/http/client.py", line 607, in _safe_read
    chunk = self.fp.read(min(amt, MAXAMOUNT))
  File "/usr/lib/python3.5/socket.py", line 575, in readinto
    return self._sock.recv_into(b)
  File "/usr/lib/python3.5/ssl.py", line 929, in recv_into
    return self.read(nbytes, buffer)
  File "/usr/lib/python3.5/ssl.py", line 791, in read
    return self._sslobj.read(len, buffer)
  File "/usr/lib/python3.5/ssl.py", line 575, in read
    v = self._sslobj.read(len, buffer)
socket.timeout: The read operation timed out

EDIT:

I noticed I missed a few lines of code thanks to @tdelaney I added them to the code above and I'm posting the solution I wrote if you post the solution or if you have a better approach to solve it I will mark the answer as correct

Solution:

for _ in range(max_retries):
    try:
        req = Request(url, headers={'User-Agent' :'Mozilla/5.0'})
        response = urlopen(req,timeout=5)
        break
    except error.URLError as err: 
        print("URL that generated the error code: ", url)
        print("Error description:",err.reason)
    except error.HTTPError as err:
        print("URL that generated the error code: ", url)
        print("Error code:", err.code)
        print("Error description:", err.reason)
    except socket.timeout:
        print("URL that generated the error code: ", url)
        print("Error description: No response.")
    except socket.error:
        print("URL that generated the error code: ", url)
        print("Error description: Socket error.")

if response.getheader('Content-Type').startswith('text/html'):
    for _ in range(max_retries):
        try:
            htmlBytes = response.read()
            htmlString = htmlBytes.decode("utf-8")
            self.feed(htmlString)
            break
        except error.URLError as err: 
            print("URL that generated the error code: ", url)
            print("Error description:",err.reason)
        except error.HTTPError as err:
            print("URL that generated the error code: ", url)
            print("Error code:", err.code)
            print("Error description:", err.reason)
        except socket.timeout:
            print("URL that generated the error code: ", url)
            print("Error description: No response.")
        except socket.error:
            print("URL that generated the error code: ", url)
            print("Error description: Socket error.")

Answer 1

The python "Requests" library uses its own set of exceptions to handle errors pertaining to the HTTP protocol as well as the socket. It automatically maps exceptions returned from it's embedded socket() functions to custom ones defined in requests.exceptions.

So the exceptions raised from this...

import Requests

try:
    req = Request("http://stackoverflow.com", headers={'User-Agent' :'Mozilla/5.0'})
    urlopen(req,timeout=5)
except Timeout:
    print "Session Timed Out!"

Are equivalent to the exceptions raised by this...

import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
    s.connect(("127.0.0.1", 80))
except socket.timeout:
    print "Session Timed Out"

Your fixed code...

for _ in range(max_retries):
try:
    req = Request(url, headers={'User-Agent' :'Mozilla/5.0'})
    response = urlopen(req,timeout=5)
    break
except error.URLError as err: 
    print("URL that generated the error code: ", url)
    print("Error description:",err.reason)
except error.HTTPError as err:
    print("URL that generated the error code: ", url)
    print("Error code:", err.code)
    print("Error description:", err.reason)
except Timeout:
    print("URL that generated the error code: ", url)
    print("Error description: Session timed out.")
except ConnectionError:
    print("URL that generated the error code: ", url)
    print("Error description: Socket error timed out.")