如何为 snap 包设置 PYTHONPATH？

我正在尝试打包一个非纯 python 项目。我使用python带有自定义构建/安装脚本的插件。

该项目包含桌面应用程序所需的 2 个 python 包：

• alfanous(API)
• alfanous-desktop（Qt PySide GUI）

snapcraft.yaml文件：

name: alfanous
version: "0.7.8"
summary: Alfanous
description: GNU hello prints a friendly greeting.
  This is part of the snapcraft tour at http://snapcraft.io/create/
#confinement: strict
confinement: devmode

apps:
  alfanous-gui:
    command: usr/bin/alfanous-desktop
    #desktop: usr/share/applications/my-app.desktop
  alfanous-cli:
    command: usr/bin/alfanous-console

parts:
  alfanous-git:
    build-packages:
      #- python
      - sqlite3
      - pyside-tools
      - qt4-linguist-tools
      - python-babel
      - qt4-qmake
      - python-setuptools
      #- python-pyparsing
      #- perl
    #plugin: make
    plugin: python
    python-version: python2
    #source: https://github.com/Alfanous-team/alfanous/archive/0.7.8.tar.gz
    source: https://github.com/Alfanous-team/alfanous.git
    source-type: git
    source-depth: 1
    #source-tag: 0.7.8
    build: |
      make build
    install: |
      echo _______#######:$(pwd)
      #make install_api 
      make install_api DESTDIR=$SNAPCRAFT_PART_INSTALL
      make install_desktop DESTDIR=$SNAPCRAFT_PART_INSTALL
    stage-packages:
      - python-pyparsing
      - python-pyside
      #- epydoc
      #- sphinx
      - python-babel
      - python-setuptools
    python-packages:
      - pyparsing
      - pyside
      - babel

snap 包的构建和安装没有错误。但是，如果我尝试运行它：

$ alfanous.alfanous-cli
Traceback (most recent call last):
  File "/snap/alfanous/x3/usr/bin/alfanous-console", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/snap/alfanous/x3/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2927, in <module>
    @_call_aside
  File "/snap/alfanous/x3/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2913, in _call_aside
    f(*args, **kwargs)
  File "/snap/alfanous/x3/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2940, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/snap/alfanous/x3/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 635, in _build_master
    ws.require(__requires__)
  File "/snap/alfanous/x3/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 943, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/snap/alfanous/x3/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 829, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'alfanous==0.7.29' distribution was not found and is required by the application

我的第一个嫌疑人是 non-complete PYTHONPATH，试图调试：

snap run --shell alfanous.alfanous-cli
env | grep -i python

什么都没有。

两个包都在那里：

$ ls /snap/alfanous/current/usr/lib/python2.7/site-packages/
alfanous                        alfanousDesktop
alfanous-0.7.29-py2.7.egg-info  alfanousDesktop-0.7.29-py2.7.egg-info

我怎样才能PYTHONPATH正确设置？python插件不应该解决这个问题吗？

snapcraft v2.28 Ubuntu 16.04.2 LTS 64Bit