ipython extension to handle an absent pwd

cd_ipy.py

"""Once this extension is installed to a ipython instance, it no longer crashes if the current directory is removed.
Based on the work of dhananjaysathe
More info at: https://github.com/ipython/ipython/pull/811"""
import os, logging, IPython, errno

def getcwdu(self):
    """Graciously handles cases when PWD does not exist.
    Defaults to home directory eliminating the OSError exception.
    """
    try:
        current_dir_path = os.getcwdu()
    except OSError as e :
        if e.errno == errno.ENOENT:
            logging.warn("Path does not exist, defaulting to Home Directory")
            os.chdir(os.path.expanduser('~'))

def load_ipython_extension(ip):
    ip.set_hook('pre_run_code_hook', getcwdu)

A couple of suggestions:

• I'm not sure that your unload_ipython_extension will work properly, and I worry that it might actually cause an infinite recursion if pre_run_code_hook tries to call itself. I'm not sure if we have a way to unregister a hook function. If not, you can leave unload_ipython_extension unimplemented: only load_ipython_extension is required.
• Does the HOME environment variable exist in all cases, including on Windows? If not, os.path.expanduser('~') may be a safer option.
• except OSError as e will make it work on Python 3 as well.
• Using errno.ENOENT in place of a literal 2 makes it slightly clearer what the code is doing.

@takluyver, I was unable to reproduce the infinite recursion when unloading cd_ipy. However, since I was unable to unload the extension at all(%unload cd_ipy didn't produce any effect) and didn't find anything related to unregistering a hook, I thought it was safe enough to simply remove the unload function as you suggested.

I did follow your other suggestions and I'm thankful for you advices(I'll use the syntax for exception catching in my future projects). I only hoped, though, that you would point out a ipython-ish way to raise a warning, the error message that my extension produce contrasts with colorful error messages of ipython :-)