How to call dependencies in snapcraft.yaml

I edited my yaml file and ran snapcraft. Alas I get an error. Is this a bug in snapcraft, in my yaml file or somewhere else?

> sudo -H snapcraft
Skipping pull trespass (already ran)
Preparing to build trespass 
Building trespass 
Collecting pip
Collecting setuptools
Collecting wheel
Installing collected packages: pip, setuptools, wheel
Successfully installed pip-9.0.1 setuptools-36.6.0 wheel-0.30.0
Staging trespass 
Priming trespass 
Traceback (most recent call last):
  File "/usr/bin/snapcraft", line 11, in <module>
    load_entry_point('snapcraft==2.34+17.10', 'console_scripts', 'snapcraft')()
  File "/usr/lib/python3/dist-packages/pkg_resources/__init__.py", line 564, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/lib/python3/dist-packages/pkg_resources/__init__.py", line 2662, in load_entry_point
    return ep.load()
  File "/usr/lib/python3/dist-packages/pkg_resources/__init__.py", line 2316, in load
    return self.resolve()
  File "/usr/lib/python3/dist-packages/pkg_resources/__init__.py", line 2322, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/usr/lib/python3/dist-packages/snapcraft/cli/__main__.py", line 19, in <module>
    run(prog_name='snapcraft')
  File "/usr/lib/python3/dist-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/usr/lib/python3/dist-packages/click/core.py", line 1043, in invoke
    return Command.invoke(self, ctx)
  File "/usr/lib/python3/dist-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/lib/python3/dist-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/usr/lib/python3/dist-packages/snapcraft/cli/__init__.py", line 110, in run
    ctx.forward(lifecyclecli.commands['snap'])
  File "/usr/lib/python3/dist-packages/click/core.py", line 553, in forward
    return self.invoke(cmd, **kwargs)
  File "/usr/lib/python3/dist-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/snapcraft/cli/lifecycle.py", line 132, in snap
    project_options, directory=directory, output=output)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/lifecycle.py", line 349, in snap
    execute('prime', project_options)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/lifecycle.py", line 130, in execute
    _Executor(config, project_options).run(step, part_names)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/lifecycle.py", line 228, in run
    self._create_meta(step, part_names)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/lifecycle.py", line 269, in _create_meta
    self.config.snapcraft_yaml_path)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/meta.py", line 84, in create_snap_packaging
    packaging.write_snap_yaml()
  File "/usr/lib/python3/dist-packages/snapcraft/internal/meta.py", line 111, in write_snap_yaml
    snap_yaml = self._compose_snap_yaml()
  File "/usr/lib/python3/dist-packages/snapcraft/internal/meta.py", line 276, in _compose_snap_yaml
    snap_yaml['apps'] = self._wrap_apps(self._config_data['apps'])
  File "/usr/lib/python3/dist-packages/snapcraft/internal/meta.py", line 385, in _wrap_apps
    self._wrap_app(app, apps[app])
  File "/usr/lib/python3/dist-packages/snapcraft/internal/meta.py", line 392, in _wrap_app
    app[k] = self._wrap_exe(app[k], '{}-{}'.format(k, name))
  File "/usr/lib/python3/dist-packages/snapcraft/internal/meta.py", line 365, in _wrap_exe
    with open(exepath, 'rb') as exefile:
FileNotFoundError: [Errno 2] No such file or directory: '/usr/bin/trespass'
kquote

Here is my current yaml

graham@graham-VirtualBox:~/trespass-snap/snap$ cat snapcraft.yaml 

name: trespass
version: '0.6.5' 
summary: A secure command line password keeper using gpg 
description: |

grade: devel
confinement: devmode

apps:
  trespass:
    command: /usr/bin/trespass

parts:
  trespass:
    plugin: python
    python-version: python3
    source: https://github.com/gps1539/trespass/archive/0.1.tar.gz
    build-packages:
      - python3-gpgme
      - python3-numpy
      - python3-pyperclip