# Buggy code
def pip(args):
    # First things first, get a recent (stable) version of pip.
    if not os.path.exists(TOX_PIP_DIR):
        subprocess.check_call(
            [
                sys.executable,
                "-m",
                "pip",
                "--disable-pip-version-check",
                "install",
                "-t",
                TOX_PIP_DIR,
                "pip",
            ]
        )
        shutil.rmtree(glob(os.path.join(TOX_PIP_DIR, "pip-*.dist-info"))[0])
    # And use that version.
    for n, a in enumerate(args):
        if not a.startswith("-"):
            if a in "install" and "-e" in args[n:]:
                args.insert(n + 1, "--no-use-pep517")
            break
    subprocess.check_call([sys.executable, os.path.join(TOX_PIP_DIR, "pip")] + args)


# Traceback (Exception)
setuptools fix_889_and_non-ascii_in_setup.cfg_take_2 $ tox -e py27
py27 create: /Users/jaraco/code/main/setuptools/.tox/py27
py27 installdeps: -rtests/requirements.txt
py27 develop-inst: /Users/jaraco/code/main/setuptools
ERROR: invocation failed (exit code 2), logfile: /Users/jaraco/code/main/setuptools/.tox/py27/log/py27-2.log
ERROR: actionid: py27
msg: developpkg
cmdargs: '/Users/jaraco/code/main/setuptools/.tox/py27/bin/pip install --exists-action w -e /Users/jaraco/code/main/setuptools'

DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7.
Obtaining file:///Users/jaraco/code/main/setuptools
Installing build dependencies: started
Installing build dependencies: finished with status 'done'
Getting requirements to build wheel: started
Getting requirements to build wheel: finished with status 'done'
Exception:
Traceback (most recent call last):
File "/Users/jaraco/code/main/setuptools/.tox/py27/lib/python2.7/site-packages/pip/_internal/cli/base_command.py", line 176, in main
status = self.run(options, args)
File "/Users/jaraco/code/main/setuptools/.tox/py27/lib/python2.7/site-packages/pip/_internal/commands/install.py", line 315, in run
resolver.resolve(requirement_set)
File "/Users/jaraco/code/main/setuptools/.tox/py27/lib/python2.7/site-packages/pip/_internal/resolve.py", line 131, in resolve
self._resolve_one(requirement_set, req)
File "/Users/jaraco/code/main/setuptools/.tox/py27/lib/python2.7/site-packages/pip/_internal/resolve.py", line 294, in _resolve_one
abstract_dist = self._get_abstract_dist_for(req_to_install)
File "/Users/jaraco/code/main/setuptools/.tox/py27/lib/python2.7/site-packages/pip/_internal/resolve.py", line 226, in _get_abstract_dist_for
req, self.require_hashes, self.use_user_site, self.finder,
File "/Users/jaraco/code/main/setuptools/.tox/py27/lib/python2.7/site-packages/pip/_internal/operations/prepare.py", line 382, in prepare_editable_requirement
abstract_dist.prep_for_dist(finder, self.build_isolation)
File "/Users/jaraco/code/main/setuptools/.tox/py27/lib/python2.7/site-packages/pip/_internal/operations/prepare.py", line 149, in prep_for_dist
reqs = self.req.pep517_backend.get_requires_for_build_wheel()
File "/Users/jaraco/code/main/setuptools/.tox/py27/lib/python2.7/site-packages/pip/_vendor/pep517/wrappers.py", line 71, in get_requires_for_build_wheel
'config_settings': config_settings
File "/Users/jaraco/code/main/setuptools/.tox/py27/lib/python2.7/site-packages/pip/_vendor/pep517/wrappers.py", line 162, in _call_hook
raise BackendUnavailable
BackendUnavailable

py27 installed: DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7.,apipkg==1.5,atomicwrites==1.2.1,attrs==18.2.0,configparser==3.7.1,contextlib2==0.5.5,coverage==4.5.2,enum34==1.1.6,execnet==1.5.0,flake8==3.6.0,funcsigs==1.0.2,futures==3.2.0,importlib-metadata==0.8,mccabe==0.6.1,mock==2.0.0,more-itertools==5.0.0,path.py==11.5.0,pathlib2==2.3.3,pbr==5.1.1,pluggy==0.8.1,py==1.7.0,pycodestyle==2.4.0,pyflakes==2.0.0,pytest==3.10.1,pytest-cov==2.6.1,pytest-fixture-config==1.4.0,pytest-flake8==1.0.3,pytest-shutil==1.4.0,pytest-virtualenv==1.4.0,scandir==1.9.0,six==1.12.0,termcolor==1.1.0,virtualenv==16.3.0,zipp==0.3.3
________________________________________________________________________________________ summary ________________________________________________________________________________________
ERROR:   py27: InvocationError for command /Users/jaraco/code/main/setuptools/.tox/py27/bin/pip install --exists-action w -e /Users/jaraco/code/main/setuptools (see /Users/jaraco/code/main/setuptools/.tox/py27/log/py27-2.log) (exited with code 2)

# Fixed code
def pip(args):
    # First things first, get a recent (stable) version of pip.
    if not os.path.exists(TOX_PIP_DIR):
        subprocess.check_call(
            [
                sys.executable,
                "-m",
                "pip",
                "--disable-pip-version-check",
                "install",
                "-t",
                TOX_PIP_DIR,
                "pip",
            ]
        )
        shutil.rmtree(glob(os.path.join(TOX_PIP_DIR, "pip-*.dist-info"))[0])
    # And use that version.
    pypath = os.environ.get("PYTHONPATH")
    pypath = pypath.split(os.pathsep) if pypath is not None else []
    pypath.insert(0, TOX_PIP_DIR)
    os.environ["PYTHONPATH"] = os.pathsep.join(pypath)
    # Disable PEP 517 support when using editable installs.
    for n, a in enumerate(args):
        if not a.startswith("-"):
            if a in "install" and "-e" in args[n:]:
                args.insert(n + 1, "--no-use-pep517")
            break
    # Fix call for setuptools editable install.
    for n, a in enumerate(args):
        if a == ".":
            args[n] = os.getcwd()
    subprocess.check_call([sys.executable, "-m", "pip"] + args, cwd=TOX_PIP_DIR)