CODEWITHSUNDEEP
pythonpython-3.xerrno
Stefano M
Stefano M

Reputation: 4818

Availability of errno module in python across different platforms

While reviewing the system library socket.py implementation I came across this code

try:
    import errno
except ImportError:
    errno = None
EBADF = getattr(errno, 'EBADF', 9)
EINTR = getattr(errno, 'EINTR', 4)

Is this code just a relic of a bygone age, or there are platforms/implementations out there for which there is no errno module?

To be more explicit, is it safe to import errno without an exception handler?

I'm interested in answers for both python 2.x and 3.x.

Edit

To clarify the question: I have to test error codes encoded in IOError exceptions raised inside the socket module. The above code, which is in the cpython code base, made me suspicious about known situations in which socket is available, but import errno would fail. Maybe a minor question, but I would like to avoid unnecessary code.

Upvotes: 5

Views: 493

Answers (2)

jfs
jfs

Reputation: 414695

errno is available since Python 1.4. The availability of the names such as ENOENT may depend on the platform: there are tons of ifdefs in the errno module source. "errno.h" header is checked in ./configure so it might not be available everywhere (it seems it is not used on WinCE) but it shouldn't prevent import errno.

Here's the initial revision that introduces errno=None:

 try:
-    from errno import EBADF
+    import errno
 except ImportError:
-    EBADF = 9
+    errno = None
+EBADF = getattr(errno, 'EBADF', 9)
+EINTR = getattr(errno, 'EINTR', 4)

I can understand the state before: from errno import EBADF may raise ImportError because EBADF might not be available on the system. The state after, I don't understand. I think import errno should be always successful on CPython on any platform.

Upvotes: 1

zmo
zmo

Reputation: 24802

well, there may be cases where errno might not be available. I did not check before saying it, but for python implementations that run on non-Unix systems, such as windows, symbian... As well as for python implementations running in emulator (like the Javascript based python REPL).

Though, if you don't provide an alternative to using errno, and actually to the use of sockets for those other systems, I'd say you can safely leave the import fail loudly, as your code won't be usable. You may just want to catch it to throw a nicer more explicit message off.

Upvotes: 1

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