socket error handling needed

If socket error occurred I think it is a timeout error or something. but It's not error raising correctly but IndexError which is not correct error MSG.

It will be fixed or None type check needed.

In the lib/socket.py 

Inside of readinto function, 576 line 
needed None type check or something

Please give us reproducible example.
Otherwise, we can't know it's our bug or it's bug of caller.

When timeout error occurred in urllib3.Poolmanager.urlopen(), the built-in TimeoutError raised which is not caught in existing timeout exception clause.

Thus, It is caught by 'error' except and it is not checking Nonetype so that raising IndexError

It patched that error and detailed in PR-5458

https://github.com/python/cpython/pull/5458

Thank you and sorry for not good at english.

It may be bug of raising TimeoutError, not catching.
That's why I want example code to reproduce.

And your screenshot doesn't contain "full" traceback chain.
It can be very important hint about who creates invalid TimeoutError.

Oh.. you are right. 
I think it's my bug. here is code
```
import urllib3
import certifi
from functools import wraps
import signal
from urllib3 import Timeout


def timeoutdec(sec):
    def decorator(func):
        def _timeout(signum, frame):
            raise TimeoutError()

        @wraps(func)
        def wrapper(*args, **kwargs):
            signal.signal(signal.SIGALRM, _timeout)
            signal.alarm(sec)
            try:
                result = func(*args, **kwargs)
            finally:
                signal.alarm(0)
            return result
        return wrapper
    return decorator


@timeoutdec(2)
def for_test():
    timeout = Timeout(connect=10.0, read=2.0)
    url = 'http://httpbin.org/delay/7'
    method = 'GET'
    body = None
    headers = None
    http = urllib3.PoolManager(timeout=timeout,
                               cert_reqs='CERT_REQUIRED',
                               ca_certs=certifi.where())
    while True:
        response = http.urlopen(method, url,
                                body=body,
                                headers=headers,
                                preload_content=True)

        print(response.data)


for_test()

```

here is the code that i got same traceback.

maybe the TimeoutError is raised from my code, timeoutdec().

I thought it was python bug. sorry for bothering you.


and I will close my PR-32729.

According to the reporter, it's not a bug in Python.