#!/usr/bin/env python

# Only needed in 2.5
from __future__ import with_statement


class Alsome(object):
    """
    An alsome object to use with a with statement.
    """

    def __enter__(self):
        """
        Executed at the point of with'ing. We return outselves so that we can
        use this object like "with Alsome() as a:"
        """
        print "Entering ..."
        return self

    def __exit__(self, ttype, value, traceback):
        """
        Executed at the end of the with statement which is either when all
        code within the with statement has been executed successfully or
        if an exception is raised.

        ttype is the type of the traceback.
        value is the value of the traceback (like a message).
        traceback is the traceback itself.
        """
        if traceback != None:
            print "Rolling back due to %s: %s" % (ttype.__name__, value)
        print "Exiting ..."

    def __init__(self):
        """
        Simple constructor.
        """
        print "Created the object ..."
        self.hello = None


if __name__ == '__main__':
    # Work
    with Alsome() as a:
        a.hello = "Hi!"
        print a.hello

    # Raise an error
    with Alsome() as a:
        a.hello = "Ho!"
        sda
        print a.hello

[steve@tachikoman ~]$ python t.py 
Created the object ...
Entering ...
Hi!
Exiting ...
Created the object ...
Entering ...
Rolling back due to NameError: name 'sda' is not defined
Exiting ...
Traceback (most recent call last):
  File "t.py", line 51, in <module>
    sda
NameError: name 'sda' is not defined
[steve@tachikoman ~]$