I'll submit a version raising an exception. The absolute path approach does sound tempting. But it appears that checking the contents of /var/lib/juju/ is another indirect way of checking what version you have (if the agents is present juju-core else legacy)

> charm dir is set in any hook, i'd consider raising an exception if its not
> set. working dir feels very implicit. ie if in an unexpected place refuse
> the temptation to guess. alternatively work out detection that's against an
> absolute path.
> 
> 
> On Fri, Apr 26, 2013 at 8:50 AM, Matthew Williams <
> <email address hidden>> wrote:
> 
> > That's a much better idea thanks, should I defult to the working dir if
> > CHARM_DIR hasn't been set?
> >
> > > Please use CHARM_DIR env var explicitly instead of assuming the hook
> > hasn't
> > > change the working dir.
> > >
> > >
> > > On Fri, Apr 26, 2013 at 6:35 AM, Matthew Williams <
> > > <email address hidden>> wrote:
> > >
> > > > Matthew Williams has proposed merging
> > > > lp:~mattyw/charm-tools/legacy_juju_call into lp:charm-tools.
> > > >
> > > > Commit message:
> > > > Added legacy_juju function with tests
> > > >
> > > > Requested reviews:
> > > >   charmers (charmers)
> > > >
> > > > For more details, see:
> > > >
> > > > https://code.launchpad.net/~mattyw/charm-
> > > tools/legacy_juju_call/+merge/161087
> > > >
> > > > A few charms I'm working on need to know if they're running under juju
> > > > (python) or juju-core. This functionality is also needed in the
> > juju-gui
> > > > charm
> > > > https://bazaar.launchpad.net/~juju-gui/charms/precise/juju-
> > > gui/trunk/view/head:/hooks/utils.pyline 103.
> > > >
> > > > It seems to me that there are a number of ways to work out which
> > version
> > > > of juju you're working under. But there should only be one correct way
> > > > which should be documented (and implemented) somewhere common. I
> > thought
> > > > putting something here might be quite useful
> > > > --
> > > >
> > > > https://code.launchpad.net/~mattyw/charm-
> > > tools/legacy_juju_call/+merge/161087
> > > > You are subscribed to branch lp:charm-tools.
> > > >
> > > > === modified file 'helpers/python/charmhelpers/__init__.py'
> > > > --- helpers/python/charmhelpers/__init__.py     2013-04-02 21:30:49
> > +0000
> > > > +++ helpers/python/charmhelpers/__init__.py     2013-04-26 10:34:24
> > +0000
> > > > @@ -22,6 +22,7 @@
> > > >             'wait_for_page_contents',
> > > >             'wait_for_relation',
> > > >             'wait_for_unit',
> > > > +           'legacy_juju',
> > > >             ]
> > > >
> > > >  from collections import namedtuple
> > > > @@ -37,6 +38,7 @@
> > > >  import urllib2
> > > >  import yaml
> > > >  from subprocess import CalledProcessError
> > > > +import os
> > > >
> > > >
> > > >  SLEEP_AMOUNT = 0.1
> > > > @@ -275,3 +277,8 @@
> > > >          if time.time() - start_time >= timeout:
> > > >              raise RuntimeError('timeout waiting for contents of ' +
> > url)
> > > >          time.sleep(SLEEP_AMOUNT)
> > > > +
> > > > +
> > > > +def legacy_juju():
> > > > +    """Return True if the charm was deployed using python juju."""
> > > > +    return not os.path.exists(os.path.join(os.getcwd(), '..',
> > > > 'agent.conf'))
> > > >
> > > > === modified file
> > 'helpers/python/charmhelpers/tests/test_charmhelpers.py'
> > > > --- helpers/python/charmhelpers/tests/test_charmhelpers.py
> >  2013-04-02
> > > > 21:30:49 +0000
> > > > +++ helpers/python/charmhelpers/tests/test_charmhelpers.py
> >  2013-04-26
> > > > 10:34:24 +0000
> > > > @@ -8,6 +8,7 @@
> > > >  from testtools import TestCase
> > > >
> > > >  import sys
> > > > +import os
> > > >  # Path hack to ensure we test the local code, not a version installed
> > in
> > > >  # /usr/local/lib.  This is necessary since /usr/local/lib is prepended
> > > > before
> > > >  # what is specified in PYTHONPATH.
> > > > @@ -470,6 +471,25 @@
> > > >          charmhelpers.log_exit()
> > > >          self.assertEqual(['<-- Exiting SCRIPT-NAME'], logged)
> > > >
> > > > +    def test_not_legacy_juju(self):
> > > > +        # The Go version of juju install an agent.conf file in the
> > > > directory
> > > > +        # above the charm. If that file exists then we must be running
> > > > against
> > > > +        # the go version of juju
> > > > +        agent_file_path = "%s/../agent.conf" % os.getcwd()
> > > > +        with open(agent_file_path, 'w') as agent_file:
> > > > +            agent_file.write("")
> > > > +        self.assertEqual(False, charmhelpers.legacy_juju())
> > > > +        os.remove(agent_file_path)
> > > > +        self.assertEqual(False, os.path.exists(agent_file_path))
> > > > +
> > > > +    def test_legacy_juju(self):
> > > > +        # The Go version of juju install an agent.conf file in the
> > > > directory
> > > > +        # above the charm. If that file doesn't exist then we must be
> > > > running
> > > > +        # against the legacy version of juju
> > > > +        agent_file_exists = os.path.exists("%s/../agent.conf" %
> > > > os.getcwd())
> > > > +        self.assertEqual(False, agent_file_exists)
> > > > +        self.assertEqual(True, charmhelpers.legacy_juju())
> > > > +
> > > >
> > > >  if __name__ == '__main__':
> > > >      unittest.main()
> > > >
> > > >
> > > >
> > --
> >
> > https://code.launchpad.net/~mattyw/charm-
> tools/legacy_juju_call/+merge/161087
> > You are subscribed to branch lp:charm-tools.
> >