arcpy_cm.py

## How I think you should do it
### this lives tucked away somewhere
import arcpy

class Extension(object):
    def __init__(self, name):
        self.name = name

    def __enter__(self):
        if arcpy.CheckExtension(self.name) == "Available":
            arcpy.CheckOutExtension(self.name)
        else:
            raise ValueError("%s license isn't available" % self.name)

    def __exit__(self, *args):
        arcpy.CheckInExtension(self.name)
            

class OverwriteState(object):
    def __init__(self, overwrite):
        self.orig_state = arcpy.env.overwriteOutput
        self.new_state = bool(overwrite)

    def __enter__(self, *args, **kwargs):
        arcpy.env.overwriteOutput = self.new_state

    def __exit__(self, *args, **kwargs):
        arcpy.env.overwriteOutput = self.orig_state


class WorkSpace(object):
    def __init__(self, path):
        self.orig_workspace = arcpy.env.workspace
        self.new_workspace = path

    def __enter__(self, *args, **kwargs):
        arcpy.env.workspace = self.new_workspace

    def __exit__(self, *args, **kwargs):
        arcpy.env.workspace = self.orig_workspace
            
            
### then you can just do this:
with Extension("3D"), OverwriteState(True), Workspace("c:/GrosMorne"):
    arcpy.HillShade_3d("WesternBrook", "wbrook_hill", 300)
    arcpy.Aspect_3d("WesternBrook", "wbrook_aspect")





#---------------------------------------------------------------
## This is how Esri recommends you to do it every. single. time.
import arcpy

class LicenseError(Exception):
    pass

try:
    if arcpy.CheckExtension("3D") == "Available":
        arcpy.CheckOutExtension("3D")
    else:
        # raise a custom exception
        raise LicenseError

    arcpy.env.workspace = "c:/GrosMorne"
    arcpy.HillShade_3d("WesternBrook", "wbrook_hill", 300)
    arcpy.Aspect_3d("WesternBrook", "wbrook_aspect")
    arcpy.CheckInExtension("3D")

except LicenseError:
    print("3D Analyst license is unavailable")
except arcpy.ExecuteError:
    print(arcpy.GetMessages(2))

arcpy_cm_fxns.py

from contextlib improt contextmanager

import arcpy

@contextmanager
def Extension(name):
    """ Context manager to facilitate the use of ArcGIS extensions

    Inside the context manager, the extension will be checked out. Once
    the interpreter leaves the code block by any means (e.g., successful
    execution, raised exception) the extension will be checked back in.

    Examples
    --------
    >>> import propagator, arcpy
    >>> with propagator.utils.Extension("spatial"):
    ...     arcpy.sa.Hillshade("C:/data/dem.tif")

    """

    if arcpy.CheckExtension(name) == u"Available":
        status = arcpy.CheckOutExtension(name)
        yield status
    else:
        raise RuntimeError("%s license isn't available" % name)

    arcpy.CheckInExtension(name)


@contextmanager
def OverwriteState(state):
    """ Context manager to temporarily set the ``overwriteOutput``
    environment variable.

    Inside the context manager, the ``arcpy.env.overwriteOutput`` will
    be set to the given value. Once the interpreter leaves the code
    block by any means (e.g., successful execution, raised exception),
    ``arcpy.env.overwriteOutput`` will reset to its original value.

    Parameters
    ----------
    path : str
        Path to the directory that will be set as the current workspace.

    Examples
    --------
    >>> from propagator import utils
    >>> with utils.OverwriteState(False):
    ...     # some operation that should fail if output already exists

    """

    orig_state = arcpy.env.overwriteOutput
    arcpy.env.overwriteOutput = bool(state)
    yield state
    arcpy.env.overwriteOutput = orig_state


@contextmanager
def WorkSpace(path):
    """ Context manager to temporarily set the ``workspace``
    environment variable.

    Inside the context manager, the `arcpy.env.workspace`_ will
    be set to the given value. Once the interpreter leaves the code
    block by any means (e.g., successful execution, raised exception),
    `arcpy.env.workspace`_ will reset to its original value.

    .. _arcpy.env.workspace: http://goo.gl/0NpeFN

    Parameters
    ----------
    path : str
        Path to the directory that will be set as the current workspace.

    Examples
    --------
    >>> import propagator
    >>> with propagator.utils.OverwriteState(False):
    ...     # some operation that should fail if output already exists

    """

    orig_workspace = arcpy.env.workspace
    arcpy.env.workspace = path
    yield path
    arcpy.env.workspace = orig_workspace

I don't think ValueError is the appropriate type — RuntimeError seems more correct

@jasonbot Does it really matter? What's the benefit of that?