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Helpers for interacting with the Snap system within a Snap

Project description

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A Python library to interact with snap configuration and properties from inside a snap.

It exposes a top-level snaphelpers.Snap object which provides access to:

  • snap details:

    >>> snap = snaphelpers.Snap()
    >>> snap.instance_name
    >>> snap.version
    >>> snap.revision
  • paths:

    >>> snap.paths.common
    >>> snap.paths.snap
    >>> snap.paths.user_common
    >>> snap.paths.user_data
  • snap-related environment variables:

    >>> pprint.pprint(dict(snap.environ))
    {'ARCH': 'amd64',
     'COMMON': '/var/snap/testapp/common',
     'DATA': '/var/snap/testapp/x1',
     'INSTANCE_KEY': '',
     'INSTANCE_NAME': 'testapp',
     'LIBRARY_PATH': '/var/lib/snapd/lib/gl:/var/lib/snapd/lib/gl32:/var/lib/snapd/void',
     'NAME': 'testapp',
     'REEXEC': '',
     'REVISION': 'x1',
     'SNAP': '/snap/testapp/x1',
     'USER_COMMON': '/home/ack/snap/testapp/common',
     'USER_DATA': '/home/ack/snap/testapp/x1',
     'VERSION': '0+git.fdf80cd'}
    >>> snap.environ.ARCH
  • configuration options:

    >>> snap.config.set({'': 'baz', 'asdf': 3})  # this needs to be run as root
    >>> options = snap.config.get_options('foo', 'asdf')
    >>> options['foo']
    {'bar': 'baz'}
    >>> options['']
    >>> options['asdf']
    >>> options.as_dict()
    {'asdf': 3, 'foo': {'bar': 'baz'}}

Hook helpers

The library provides helpers to reduce boilerplate when setting up hooks for the snap.

Hooks can be defined by simply registering functions to be called as hooks via entry_points in the application

    # ...
        'snaphelpers.hooks': [
            'configure = testapp:configure_hook',
            'install = testapp:install_hook'

Hook functions are called with a Snap object as argument:

def install_hook(snap: snaphelpers.Snap):
    # ...

def configure_hook(snap: snaphelpers.Snap):
    # ...

snap-helpers will take care of the hooks plumbing (i.e. creating hook files in $SNAP/snap/hooks).

Testing with the snap

The snap-helpers snap provides a way to easily test code using the library in a real snap environment with strict confinement.

It provides the python and ipython commands:

$ snap-helpers.python -c 'from pprint import pprint; import snaphelpers; pprint(dict(snaphelpers.SnapEnviron()))'
{'ARCH': 'amd64',
 'COMMON': '/var/snap/snap-helpers/common',
 'DATA': '/var/snap/snap-helpers/x1',
 'INSTANCE_NAME': 'snap-helpers',
 'LIBRARY_PATH': '/var/lib/snapd/lib/gl:/var/lib/snapd/lib/gl32:/var/lib/snapd/void',
 'NAME': 'snap-helpers',
 'REEXEC': '',
 'REVISION': 'x1',
 'SNAP': '/snap/snap-helpers/x1',
 'USER_COMMON': '/home/ack/snap/snap-helpers/common',
 'USER_DATA': '/home/ack/snap/snap-helpers/x1',
 'VERSION': '0+git.26e1e9d'}

The snap can be built and installed as follows:

$ snapcraft
$ sudo snap install --dangerous snap-helpers_*.snap


snap-helpers can be installed from PyPI.


$ pip install snap-helpers


Full documentation is available on ReadTheDocs.

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