pip3 10.0.0 installs a pip binary causing conflicts with python2

[dbxgil]

• Pip version: 10.0.0
• Python version: 3.6.5
• Operating system: macOS 10.13.4 (17E199)

Description:

When you upgrade pip3 from 9.0.3 to 10.0.0 pip3 installs an additional pip binary. This causes a conflict with coexistence of Python 2.7.x installations; contrary to the Python project's intentions. From the Python project's README file:

Python 3 and Python 2 Co-existence

Python.org Python 3.6 and 2.7.x versions can both be installed on your system and will not conflict. Command names for Python 3 contain a 3 in them, python3 (or python3.6), idle3 (or idle3.6), pip3 (or pip3.6), etc. Python 2.7 command names contain a 2 or no digit: python2 (or python2.7 or python), idle2 (or idle2.7 or idle), etc.

The release notes for Python2.7.14 have a similarly worded note on Python 3 and Python 2 co-existence.

For additional reference see: https://bugs.python.org/issue33290

What I've run:

gilw-mbp:bin gilw$ ls -al pip*
-rwxrwxr-x  1 root  admin  253 Apr 17 09:21 pip3
-rwxrwxr-x  1 root  admin  253 Apr 17 09:21 pip3.6

gilw-mbp:bin gilw$ pip3 install --upgrade pip
Collecting pip
  Downloading https://files.pythonhosted.org/packages/62/a1/0d452b6901b0157a0134fd27ba89bf95a857fbda64ba52e1ca2cf61d8412/pip-10.0.0-py2.py3-none-any.whl (1.3MB)
    100% |████████████████████████████████| 1.3MB 1.0MB/s
Installing collected packages: pip
  Found existing installation: pip 9.0.3
    Uninstalling pip-9.0.3:
      Successfully uninstalled pip-9.0.3
Successfully installed pip-10.0.0
gilw-mbp:bin gilw$ ls -al pip*
-rwxr-xr-x  1 gilw  admin  263 Apr 17 09:23 pip
-rwxr-xr-x  1 gilw  admin  263 Apr 17 09:23 pip3
-rwxr-xr-x  1 gilw  admin  263 Apr 17 09:23 pip3.6

[gvanrossum]

This bites me regularly. Since the Python 3 installer does not install a 'pip' binary (only 'pip3'), something like 'pip3 install -U pip' should not either.

See also https://github.com/python/cpython/pull/6683 and https://bugs.python.org/issue33290 (showing that the CPython team does consider this a bug).

[pradyunsg]

@pfmoore @ncoghlan Any thoughts on how we could achieve this?

I'm not sure if not installing pip on Python 3 as a solution here (because that's what we want in virtual environments).

[gvanrossum]

But pip can tell whether it's installing into a virtualenv or not, right?

[ncoghlan]

The way we handle this in ensurepip is via a separate --default-pip flag that controls whether or not the pip command gets installed: https://docs.python.org/3/library/ensurepip.html#command-line-interface

To actually let that work, there's a bunch of special casing in https://github.com/pypa/pip/blob/0ae0109901f63b7f133229a9fee41332dd7366b4/src/pip/_internal/wheel.py#L390 that checks the ENSUREPIP_OPTIONS environment variable when installing pip itself.

So I think to improve this situation, the key would be to change the way that special casing works when ENSUREPIP_OPTIONS isn't set.

Specifically, what I would suggest is that when outside a virtual environment, pip could check for shutil.which('python') == sys.executable, and if that's not true, then treat it like ENSUREPIP_OPTIONS=install (thus setting pipX and pipX.Y, but not pip)

[dstufft]

I'm hesitant to add even more special casing for pip here, especially one that I think is just going to shift some of the confusion around and make some cases better and some worse. This is realistically a special case of the issues described in https://github.com/pypa/pip/issues/3164, so I'm going to close this in favor of further discussion over there.

[lock[bot]]

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