Question

As far as I know, most of the errnos returned by python’s exceptions are the same with the errnos in “linux/errno.h”. But at sometimes, things are not like what I expect:

For example, when a socket connection throw a socket.timeout exception, the errno it returned should be 110, however, it’s errno is always None:

try:
    address = ('8.8.8.8', 12345)  
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 
    s.settimeout(1)
    s.connect(address)  
except EnvironmentError as e:
    print e.errno      # None
    print e.strerror   # "time out"

Secondly, when a address-related exception is throwed, the errno will be negative, but the errnos in linux/errno.h are between 1 and 133:

try:
    address = ('xxxxxxx', 12345)
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect(address)
except socket.gaierror, v:
    print v[0]     # -5

In this case, will print -5.

I’m so confused of all of these errnos. 🙁

Answer 1

Only OSError and IOError carry an errno value. The socket.gaierror will return a getaddrinfo(3) error code. Other exceptions usually just carry strings. The codes are in the socket module. the -5 is socket.EAI_NODATA, which means “The specified network host exists, but does not have any network addresses defined”.