pip自体を更新する（pip install --upgrade pip）

　古いと問題になることがあるらしいので。

$ pip -V
pip 18.1 from /usr/lib/python2.7/dist-packages/pip (python 2.7)
$ pip3 -V
pip 18.1 from /usr/lib/python3/dist-packages/pip (python 3.7)

$ pip install --upgrade pip
Looking in indexes: https://pypi.org/simple, https://www.piwheels.org/simple
Collecting pip
  Downloading https://files.pythonhosted.org/packages/00/b6/9cfa56b4081ad13874b0c6f96af8ce16cfbc1cb06bedf8e9164ce5551ec1/pip-19.3.1-py2.py3-none-any.whl (1.4MB)
    100% |████████████████████████████████| 1.4MB 236kB/s 
Installing collected packages: pip
Successfully installed pip-19.3.1

$ pip3 install --upgrade pip
Looking in indexes: https://pypi.org/simple, https://www.piwheels.org/simple
Collecting pip
  Using cached https://files.pythonhosted.org/packages/00/b6/9cfa56b4081ad13874b0c6f96af8ce16cfbc1cb06bedf8e9164ce5551ec1/pip-19.3.1-py2.py3-none-any.whl
Installing collected packages: pip
Successfully installed pip-19.3.1

対象環境

• 2020-01-12
• Raspbierry pi 4 Model B
• Raspbian buster 10.0 2019-09-26 ※
• bash 5.0.3(1)-release

$ uname -a
Linux raspberrypi 4.19.75-v7l+ #1270 SMP Tue Sep 24 18:51:41 BST 2019 armv7l GNU/Linux