PIB

Jupyter notebook が使いたかったのだが、Ubuntu 16.04.6 LTS の公式リポジトリにはそれらしいのがなかったため、
pip3 で入れようとしたところ以下のように言われた。

$ pip3 install jupyter
プログラム 'pip3' はまだインストールされていません。 次のように入力することでインストールできます:
sudo apt install python3-pip

言われるがまま、

sudo apt install python3-pip

として pip3 を導入した後再度 install を試みたところ

$ pip3 install jupyter
Collecting jupyter
  Downloading https://files.pythonhosted.org/packages/83/df/0f5dd132200728a86190397e1ea87cd76244e42d39ec5e88efd25b2abd7e/jupyter-1.0.0-py2.py3-none-any.whl
...
Successfully built pandocfilters tornado prometheus-client backcall pyrsistent
Installing collected packages: pyzmq, ipython-genutils, decorator, six, traitlets, jupyter-core, attrs, pyrsistent, setuptools, jsonschema, nbformat, pygments, webencodings, bleach, testpath, entrypoints, mistune, MarkupSafe, jinja2, defusedxml, pandocfilters, nbconvert, tornado, Send2Trash, python-dateutil, jupyter-client, pickleshare, ptyprocess, pexpect, wcwidth, prompt-toolkit, parso, jedi, backcall, ipython, ipykernel, terminado, prometheus-client, notebook, widgetsnbextension, ipywidgets, qtconsole, jupyter-console, jupyter
Successfully installed MarkupSafe-0.23 Send2Trash attrs backcall bleach decorator-4.0.6 defusedxml entrypoints ipykernel ipython-2.4.1 ipython-genutils ipywidgets jedi-0.9.0 jinja2-2.8 jsonschema jupyter jupyter-client jupyter-console jupyter-core mistune nbconvert nbformat notebook pandocfilters parso pexpect-4.0.1 pickleshare prometheus-client prompt-toolkit ptyprocess-0.5 pygments-2.1 pyrsistent python-dateutil-2.4.2 pyzmq-15.2.0 qtconsole setuptools-20.7.0 six-1.10.0 terminado testpath tornado traitlets wcwidth webencodings widgetsnbextension
You are using pip version 8.1.1, however version 19.1.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

のように成功したのだが、 pip を upgrade しろというので言われるがままに upgrade してみると

$ pip3 install --upgrade pip
Collecting pip
  Downloading https://files.pythonhosted.org/packages/5c/e0/be401c003291b56efc55aeba6a80ab790d3d4cece2778288d65323009420/pip-19.1.1-py2.py3-none-any.whl (1.4MB)
    100% |████████████████████████████████| 1.4MB 1.5MB/s 
Installing collected packages: pip
Successfully installed pip-19.1.1

のように成功したように見えたのだが、
なぜか pip3 が以下のようにまともに動かなくなってしまった。

$ pip3
Traceback (most recent call last):
  File "/usr/bin/pip3", line 9, in <module>
    from pip import main
ImportError: cannot import name 'main'

やる気なくしたので自棄糞気味に「Traceback (most recent call last): File "/usr/bin/pip3", line 9, in [module] from pip import main ImportError: cannot import name 'main'」とかググってみると以下のページが見つかった。

• KOKENSHAの技術ブログ / 2018-06-19: Python pip3 – pip upgradeした後 「cannot import name ‘main’ 」error

.deb でパッケージ提供されてる物を、pip3 で更新して上書きしちゃダメとの事。

上記ページでは、sudo して python で uninstall pip してから apt で再度 install してるけど、
ユーザーモードで pip upgrade したためか、以下のようにユーザーモードで python から uninstall pip するだけで、apt による再 install はしなくても復旧した。

$ python3 -m pip uninstall pip
Uninstalling pip-19.1.1:
  Would remove:
    /home/kou/.local/bin/pip
    /home/kou/.local/bin/pip3
    /home/kou/.local/bin/pip3.5
    /home/kou/.local/lib/python3.5/site-packages/pip-19.1.1.dist-info/*
    /home/kou/.local/lib/python3.5/site-packages/pip/*
Proceed (y/n)? 
Your response ('') was not one of the expected responses: y, n
Proceed (y/n)? y
  Successfully uninstalled pip-19.1.1

$ pip3

Usage:   
  pip <command> [options]

Commands:
  install                     Install packages.
  download                    Download packages.
  uninstall                   Uninstall packages.
  freeze                      Output installed packages in requirements format.
  list                        List installed packages.
  show                        Show information about installed packages.
  search                      Search PyPI for packages.
  wheel                       Build wheels from your requirements.
  hash                        Compute hashes of package archives.
  completion                  A helper command used for command completion
  help                        Show help for commands.

General Options:
  -h, --help                  Show help.
  --isolated                  Run pip in an isolated mode, ignoring
                              environment variables and user configuration.
  -v, --verbose               Give more output. Option is additive, and can be
                              used up to 3 times.
  -V, --version               Show version and exit.
  -q, --quiet                 Give less output.
  --log <path>                Path to a verbose appending log.
  --proxy <proxy>             Specify a proxy in the form
                              [user:passwd@]proxy.server:port.
  --retries <retries>         Maximum number of retries each connection should
                              attempt (default 5 times).
  --timeout <sec>             Set the socket timeout (default 15 seconds).
  --exists-action <action>    Default action when a path already exists:
                              (s)witch, (i)gnore, (w)ipe, (b)ackup.
  --trusted-host <hostname>   Mark this host as trusted, even though it does
                              not have valid or any HTTPS.
  --cert <path>               Path to alternate CA bundle.
  --client-cert <path>        Path to SSL client certificate, a single file
                              containing the private key and the certificate
                              in PEM format.
  --cache-dir <dir>           Store the cache data in <dir>.
  --no-cache-dir              Disable the cache.
  --disable-pip-version-check
                              Don't periodically check PyPI to determine
                              whether a new version of pip is available for
                              download. Implied with --no-index.