How to get the errno of an IOError?

Question

C has perror and errno, which print and store the last error encountered. This is convenient when doing file io as I do not have to fstat() every file that fails as an argument to fopen() to present the user with a reason why the call failed.

I was wondering what is the proper way to grab errno when gracefully handling the IOError exception in python?

In [1]: fp = open("/notthere")
---------------------------------------------------------------------------
IOError                                   Traceback (most recent call last)

/home/mugen/ in ()

IOError: [Errno 2] No such file or directory: '/notthere'


In [2]: fp = open("test/testfile")
---------------------------------------------------------------------------
IOError                                   Traceback (most recent call last)

/home/mugen/ in ()

IOError: [Errno 13] Permission denied: 'test/testfile'


In [5]: try:
   ...:     fp = open("nothere")
   ...: except IOError:
   ...:     print "This failed for some reason..."
   ...:     
   ...:     
This failed for some reason...

Answer 1

The Exception has an errno attribute:

try:
    fp = open("nothere")
except IOError as e:
    print(e.errno)
    print(e)

Answer 2

Here's how you can do it. Also see the errno module and os.strerror function for some utilities.

import os, errno

try:
    f = open('asdfasdf', 'r')
except IOError as ioex:
    print 'errno:', ioex.errno
    print 'err code:', errno.errorcode[ioex.errno]
    print 'err message:', os.strerror(ioex.errno)

• http://docs.python.org/library/errno.html
• http://docs.python.org/library/os.html

For more information on IOError attributes, see the base class EnvironmentError:

• http://docs.python.org/library/exceptions.html?highlight=ioerror#exceptions.EnvironmentError

Answer 3

try:
    fp = open("nothere")
except IOError as err:
    print err.errno 
    print err.strerror

Answer 4

Different exceptions can also be tested for in the same 'except' clause, e.g.

try:
    serial_port.open()
except (AttributeError, SerialException) as e:
    print('cannot open serial port: {}'.format(e))