#!/usr/bin/env python
#
# vm_context_manager.py - Context manager for virtual machine definitions
#
# September 2013, Glenn F. Matthews
# Copyright (c) 2013-2016 the COT project developers.
# See the COPYRIGHT.txt file at the top-level directory of this distribution
# and at https://github.com/glennmatthews/cot/blob/master/COPYRIGHT.txt.
#
# This file is part of the Common OVF Tool (COT) project.
# It is subject to the license terms in the LICENSE.txt file found in the
# top-level directory of this distribution and at
# https://github.com/glennmatthews/cot/blob/master/LICENSE.txt. No part
# of COT, including this file, may be copied, modified, propagated, or
# distributed except according to the terms contained in the LICENSE.txt file.
"""Context manager for virtual machine definitions."""
import logging
from COT.vm_factory import VMFactory
logger = logging.getLogger(__name__)
[docs]class VMContextManager(object):
"""Context manager for virtual machine definitions.
When the context manager exits, unless an error occurred, the virtual
machine's :meth:`write` method is called. Regardless of whether an error
occurred, the virtual machine's :meth:`destroy` method is then called.
Use as follows:
::
with VMContextManager(input_file, output_file) as vm:
vm.foo()
vm.bar()
For the parameters, see :class:`~COT.vm_description.VMDescription`.
"""
[docs] def __init__(self, input_file, output_file=None):
"""Create a VM instance.
For the parameters, see :class:`~COT.vm_description.VMDescription`.
"""
self.obj = VMFactory.create(input_file, output_file)
def __enter__(self):
"""Use the VM instance as the context manager object."""
return self.obj
def __exit__(self, exc_type, exc_value, trace):
"""If the block exited cleanly, write the VM out to disk.
In any case, destroy the VM.
For the parameters, see :mod:`contextlib`.
"""
# Did we exit cleanly?
try:
if exc_type is None:
self.obj.write()
finally:
self.obj.destroy()