Error after upgrading pip: cannot import name 'main'

You must have inadvertently upgraded your system pip (probably through something like sudo pip install pip --upgrade)

pip 10.x adjusts where its internals are situated. The pip3 command you're seeing is one provided by your package maintainer (presumably debian based here?) and is not a file managed by pip.

You can read more about this on pip's issue tracker

You'll probably want to not upgrade your system pip and instead use a virtualenv.

To recover the pip3 binary you'll need to sudo python3 -m pip uninstall pip && sudo apt install python3-pip --reinstall.

If you want to continue in "unsupported territory" (upgrading a system package outside of the system package manager), you can probably get away with python3 -m pip ... instead of pip3.

We can clear the error by modifying the pip file.

Check the location of the file:

$ which pip

path -> /usr/bin/pip

Go to that location(/usr/bin/pip) and open terminal

Enter: $ sudo nano pip

You can see:

import sysfrom pip import mainif __name__ == '__main__':     sys.exit(main())

Change to:

import sysfrom pip import __main__if __name__ == '__main__':     sys.exit(__main__._main())

then ctrl + o write the changes and exit

Hope this will do!!

For Ubuntu family, Debian, Linux Mint users

Thanks to Anthony's explanation above, you can retain your original system pip (in /usr/bin/ and dist-packages/) and remove the manually-installed pip (in ~/.local/) to resolve the conflict:

$ python3 -m pip uninstall pip

Ubuntu/Debian pip v8.1.1 (16.04) from python3-pip debian package (see$ pip3 -V) shows the same search results as the latest pip v10.0.1, and installs latest modules from PyPI just fine. It has a working pip command (already in the $PATH), plus the nice --user option patched-in by default since 2016. Looking at pip release notes, the newer versions are mostly about use-case specific bug fixes and certain new features, so not everyone has to rush upgrading pip just yet. And the new pip 10 can be deployed to Python virtualenvs, anyway.

But regardless of pips, your OS allows to quickly install common Python modules (including numpy) with APT, without the need for pip, for example:
$ sudo apt install python3-numpy python3-scipy (with system dependencies)
$ sudo apt install python3-pip (Debian-patched pip, slightly older but it doesn't matter)

Quick apt syntax reminder (please see man apt for details):
$ sudo apt update (to resync Ubuntu package index files from up-to-date sources)
$ apt search <python-package-name> (full text-search on all available packages)
$ apt show <python-package-name> (displays the detailed package description)
$ sudo apt install <python-package-name>

Package names prefixed with python- are for Python 2; and prefixed with python3- are for Python 3 (e.g. python3-pandas). There are thousands, and they undergo integration testing within Debian and Ubuntu. Unless you seek to install at per-user level (pip install --user option) or within virtualenv/venv, apt could be what you needed. These system packages are accessible from virtual envs too, as virtualenv will gracefully fall back to using system libs on import if your envs don't have given copies of modules.Your custom-installed (with pip --user) per-user modules in ~/.local/lib will override them too.

Note, since this is a system-wide installation, you'd rarely need to remove them (need to be mindful about OS dependencies). This is convenient for packages with many system dependencies (such as with scipy or matplotlib), as APT will keep track and provide all required system libs and C extensions, while with pip you have no such guarantees.

In fact, for system-wide Python packages (in contrast to per-user, home dir level, or lower), Ubuntu expects using the APT package manager (rather than sudo pip) to avoid breaking OS: sudo pip3 targets the very same /usr/lib/python3/dist-packages directory where APT stores OS-sensitive modules. Recent Debian/Ubuntu releases depend heavily on Python 3, so its pre-installed modules are managed by apt and shouldn't be changed.

So if you use pip3 install command, please ensure that it runs in an isolated virtual dev environment, such as with virtualenv (sudo apt install python3-virtualenv), or with Python3 built-in (-m venv), or at a per-user level (--user pip option, default in Ubuntu-provided pip since 2016), but not system-wide (never sudo pip3!), because pip interferes with the operation of the APT package manager and may affect Ubuntu OS components when a system-used python module is unexpectedly changed. Good luck!

P. S. All the above is for the 'ideal' solution (Debian/Ubuntu way).

If you still want to use the new pip3 v10 exclusively, there are 3 quick workarounds:

• simply open a new bash session (a new terminal tab, or type bash) - and pip3 v10 becomes available (see pip3 -V). debian's pip3 v8 remains installed but is broken; or
• the command $ hash -d pip3 && pip3 -V to refresh pip3 pathname in the $PATH. debian's pip3 v8 remains installed but is broken; or
• the command $ sudo apt remove python3-pip && hash -d pip3 to uninstall debian's pip3 v8 completely, in favor of your new pip3 v10.

Note: You will always need to add --user flag to any non-debian-provided pip, unless you are in a virtualenv! (it deploys python packages to ~/.local/, default in debian/ubuntu-provided python3-pip and python-pip since 2016). Your use of pip 10 system-wide, outside of virtualenv, is not really supported by Ubuntu/Debian. Never sudo pip3!

Further details:
https://github.com/pypa/pip/issues/5221#issuecomment-382069604
https://github.com/pypa/pip/issues/5240#issuecomment-381673100