Editable mode fails to install in Python 3

[buddly27]

Package installation fails in editable mode when targeting Python 3

Traceback (most recent call last):
  File "/Users/jeremyr/.virtualenvs/qip-p38/bin/qip", line 33, in <module>
    sys.exit(load_entry_point('qip-installer', 'console_scripts', 'qip')())
  File "/Users/jeremyr/dev/github/qip/source/qip/__main__.py", line 8, in main
    qip.command_line.main(prog_name="qip")
  File "/Users/jeremyr/.virtualenvs/qip-p38/lib/python3.8/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/Users/jeremyr/.virtualenvs/qip-p38/lib/python3.8/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/Users/jeremyr/.virtualenvs/qip-p38/lib/python3.8/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/jeremyr/.virtualenvs/qip-p38/lib/python3.8/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/jeremyr/.virtualenvs/qip-p38/lib/python3.8/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/Users/jeremyr/dev/github/qip/source/qip/command_line.py", line 161, in install
    qip.install(
  File "/Users/jeremyr/dev/github/qip/source/qip/__init__.py", line 139, in install
    qip.definition.export(
  File "/Users/jeremyr/dev/github/qip/source/qip/definition.py", line 38, in export
    definition = qip.definition.retrieve(mapping)
  File "/Users/jeremyr/dev/github/qip/source/qip/definition.py", line 105, in retrieve
    mapping["location"], mapping["module_name"], "package_data", "wiz.json"
KeyError: 'location'

It seems to be because editable installation provides the easy-install.pth file without the site.py in Python 3. This leads the pip show command to fail to return metadata.

[buddly27]

Setuptools 49.0.0 has indeed dropped installation of the site.py file.
https://github.com/pypa/setuptools/blob/master/CHANGES.rst#v4900

I guess we should manually parse it to set the environment variable then