pip: pip install fails with `ImportError: No module named pip._vendor` in pip==19.0.1

Environment

• pip version: 19.0.1
• Python version: 2.7.14
• OS: Debian GNU/Linux

Description

Hi guys, I ran into an unexpected pip install failure for a specific package after my CI silently upgraded pip to 19.0.1 (The problem is also present in pip==19.0 for what it is worth).

I am posting this as a new issue since it started to occur after an upgrade to pip, albeit I understand it may be an underlying issue with pendulum==1.4.4.

Thank you for reading this in advance!

Expected behavior

The following should succeed in a clean env with python 2.7.14 and pip 19:

pip install pendulum==1.4.4

How to Reproduce

This issue can be reproduced in a docker container stemming from the official python:2.7.14 docker image:

omarkhan$ docker run -it python:2.7.14 bash                                                                         omarkhan@Rion  6:19PM

root@a2286abe06a1:/# pip install -U pip
Collecting pip
  Downloading https://files.pythonhosted.org/packages/46/dc/7fd5df840efb3e56c8b4f768793a237ec4ee59891959d6a215d63f727023/pip-19.0.1-py2.py3-none-any.whl (1.4MB)
    100% |████████████████████████████████| 1.4MB 3.5MB/s
Installing collected packages: pip
  Found existing installation: pip 10.0.1
    Uninstalling pip-10.0.1:
      Successfully uninstalled pip-10.0.1
Successfully installed pip-19.0.1

root@a2286abe06a1:/# pip install pendulum==1.4.4
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.
Collecting pendulum==1.4.4
  Downloading https://files.pythonhosted.org/packages/85/a5/9fc15751f9725923b170ad37d6c61031fc9e941bafd5288ca6ee51233284/pendulum-1.4.4.tar.gz (74kB)
    100% |████████████████████████████████| 81kB 502kB/s
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  Complete output from command /usr/local/bin/python /usr/local/lib/python2.7/site-packages/pip/_vendor/pep517/_in_process.py get_requires_for_build_wheel /tmp/tmpGuP1ar:
  Traceback (most recent call last):
    File "/usr/local/lib/python2.7/site-packages/pip/_vendor/pep517/_in_process.py", line 207, in <module>
      main()
    File "/usr/local/lib/python2.7/site-packages/pip/_vendor/pep517/_in_process.py", line 197, in main
      json_out['return_val'] = hook(**hook_input['kwargs'])
    File "/usr/local/lib/python2.7/site-packages/pip/_vendor/pep517/_in_process.py", line 54, in get_requires_for_build_wheel
      return hook(config_settings)
    File "/tmp/pip-build-env-_krb5E/overlay/lib/python2.7/site-packages/setuptools/build_meta.py", line 115, in get_requires_for_build_wheel
      return _get_build_requires(config_settings, requirements=['wheel'])
    File "/tmp/pip-build-env-_krb5E/overlay/lib/python2.7/site-packages/setuptools/build_meta.py", line 101, in _get_build_requires
      _run_setup()
    File "/tmp/pip-build-env-_krb5E/overlay/lib/python2.7/site-packages/setuptools/build_meta.py", line 85, in _run_setup
      exec(compile(code, __file__, 'exec'), locals())
    File "setup.py", line 47, in <module>
      from build import *
    File "/usr/local/lib/python2.7/site-packages/pip/_vendor/pep517/build.py", line 7, in <module>
      from pip._vendor import pytoml
  ImportError: No module named pip._vendor

  ----------------------------------------
Command "/usr/local/bin/python /usr/local/lib/python2.7/site-packages/pip/_vendor/pep517/_in_process.py get_requires_for_build_wheel /tmp/tmpGuP1ar" failed with error code 1 in /tmp/pip-install-ZDj3kd/pendulum

Notes

pip installing pendulum==1.4.4 in the packaged version of pip in a official python:2.7.14 docker container works as expected:

omarkhan$ docker run -it python:2.7.14 bash                                                                         omarkhan@Rion  6:20PM

root@39354b1b100d:/# pip list
Package    Version
---------- -------
pip        10.0.1
setuptools 39.1.0
virtualenv 15.2.0
wheel      0.31.0
You are using pip version 10.0.1, however version 19.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

root@39354b1b100d:/# pip install pendulum==1.4.4
Collecting pendulum==1.4.4
  Downloading https://files.pythonhosted.org/packages/85/a5/9fc15751f9725923b170ad37d6c61031fc9e941bafd5288ca6ee51233284/pendulum-1.4.4.tar.gz (74kB)
    100% |████████████████████████████████| 81kB 2.9MB/s
  Installing build dependencies ... done
Collecting python-dateutil<3.0.0.0,>=2.6.0.0 (from pendulum==1.4.4)
  Downloading https://files.pythonhosted.org/packages/74/68/d87d9b36af36f44254a8d512cbfc48369103a3b9e474be9bdfe536abfc45/python_dateutil-2.7.5-py2.py3-none-any.whl (225kB)
    100% |████████████████████████████████| 235kB 7.1MB/s
Collecting tzlocal<2.0.0.0,>=1.5.0.0 (from pendulum==1.4.4)
  Downloading https://files.pythonhosted.org/packages/cb/89/e3687d3ed99bc882793f82634e9824e62499fdfdc4b1ae39e211c5b05017/tzlocal-1.5.1.tar.gz
Collecting pytzdata>=2018.3.0.0 (from pendulum==1.4.4)
  Downloading https://files.pythonhosted.org/packages/46/8b/d7fe0c5b24870438d5ed59ceab72d537c5374d7db3cc57107e4a922b3a23/pytzdata-2018.7-py2.py3-none-any.whl (971kB)
    100% |████████████████████████████████| 972kB 4.2MB/s
Collecting six>=1.5 (from python-dateutil<3.0.0.0,>=2.6.0.0->pendulum==1.4.4)
  Downloading https://files.pythonhosted.org/packages/73/fb/00a976f728d0d1fecfe898238ce23f502a721c0ac0ecfedb80e0d88c64e9/six-1.12.0-py2.py3-none-any.whl
Collecting pytz (from tzlocal<2.0.0.0,>=1.5.0.0->pendulum==1.4.4)
  Downloading https://files.pythonhosted.org/packages/61/28/1d3920e4d1d50b19bc5d24398a7cd85cc7b9a75a490570d5a30c57622d34/pytz-2018.9-py2.py3-none-any.whl (510kB)
    100% |████████████████████████████████| 512kB 8.0MB/s
Building wheels for collected packages: pendulum, tzlocal
  Running setup.py bdist_wheel for pendulum ... done
  Stored in directory: /root/.cache/pip/wheels/2f/4c/cd/f0cabf03ccb7edd9002875db9001108b33ebfc60b4ff9a61ae
  Running setup.py bdist_wheel for tzlocal ... done
  Stored in directory: /root/.cache/pip/wheels/15/ae/df/a67bf1ed84e9bf230187d36d8dcfd30072bea0236cb059ed91
Successfully built pendulum tzlocal
Installing collected packages: six, python-dateutil, pytz, tzlocal, pytzdata, pendulum
Successfully installed pendulum-1.4.4 python-dateutil-2.7.5 pytz-2018.9 pytzdata-2018.7 six-1.12.0 tzlocal-1.5.1
You are using pip version 10.0.1, however version 19.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

It also works in pip==18.1:

omarkhan$ docker run -it python:2.7.14 bash                                                                         omarkhan@Rion  6:20PM

root@51c149c9b52a:/# pip install pip==18.1
Collecting pip==18.1
  Downloading https://files.pythonhosted.org/packages/c2/d7/90f34cb0d83a6c5631cf71dfe64cc1054598c843a92b400e55675cc2ac37/pip-18.1-py2.py3-none-any.whl (1.3MB)
    100% |████████████████████████████████| 1.3MB 13.3MB/s
Installing collected packages: pip
  Found existing installation: pip 10.0.1
    Uninstalling pip-10.0.1:
      Successfully uninstalled pip-10.0.1
Successfully installed pip-18.1
You are using pip version 18.1, however version 19.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

root@51c149c9b52a:/# pip install pendulum==1.4.4
Collecting pendulum==1.4.4
  Downloading https://files.pythonhosted.org/packages/85/a5/9fc15751f9725923b170ad37d6c61031fc9e941bafd5288ca6ee51233284/pendulum-1.4.4.tar.gz (74kB)
    100% |████████████████████████████████| 81kB 2.1MB/s
  Installing build dependencies ... done
Collecting python-dateutil<3.0.0.0,>=2.6.0.0 (from pendulum==1.4.4)
  Downloading https://files.pythonhosted.org/packages/74/68/d87d9b36af36f44254a8d512cbfc48369103a3b9e474be9bdfe536abfc45/python_dateutil-2.7.5-py2.py3-none-any.whl (225kB)
    100% |████████████████████████████████| 235kB 4.7MB/s
Collecting tzlocal<2.0.0.0,>=1.5.0.0 (from pendulum==1.4.4)
  Downloading https://files.pythonhosted.org/packages/cb/89/e3687d3ed99bc882793f82634e9824e62499fdfdc4b1ae39e211c5b05017/tzlocal-1.5.1.tar.gz
Collecting pytzdata>=2018.3.0.0 (from pendulum==1.4.4)
  Downloading https://files.pythonhosted.org/packages/46/8b/d7fe0c5b24870438d5ed59ceab72d537c5374d7db3cc57107e4a922b3a23/pytzdata-2018.7-py2.py3-none-any.whl (971kB)
    100% |████████████████████████████████| 972kB 13.6MB/s
Collecting six>=1.5 (from python-dateutil<3.0.0.0,>=2.6.0.0->pendulum==1.4.4)
  Downloading https://files.pythonhosted.org/packages/73/fb/00a976f728d0d1fecfe898238ce23f502a721c0ac0ecfedb80e0d88c64e9/six-1.12.0-py2.py3-none-any.whl
Collecting pytz (from tzlocal<2.0.0.0,>=1.5.0.0->pendulum==1.4.4)
  Downloading https://files.pythonhosted.org/packages/61/28/1d3920e4d1d50b19bc5d24398a7cd85cc7b9a75a490570d5a30c57622d34/pytz-2018.9-py2.py3-none-any.whl (510kB)
    100% |████████████████████████████████| 512kB 2.2MB/s
Building wheels for collected packages: pendulum, tzlocal
  Running setup.py bdist_wheel for pendulum ... done
  Stored in directory: /root/.cache/pip/wheels/2f/4c/cd/f0cabf03ccb7edd9002875db9001108b33ebfc60b4ff9a61ae
  Running setup.py bdist_wheel for tzlocal ... done
  Stored in directory: /root/.cache/pip/wheels/15/ae/df/a67bf1ed84e9bf230187d36d8dcfd30072bea0236cb059ed91
Successfully built pendulum tzlocal
Installing collected packages: six, python-dateutil, pytz, tzlocal, pytzdata, pendulum
Successfully installed pendulum-1.4.4 python-dateutil-2.7.5 pytz-2018.9 pytzdata-2018.7 six-1.12.0 tzlocal-1.5.1
You are using pip version 18.1, however version 19.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.