Mac OS下升级pip-亲测ok

#新晋python小白，写下的菜鸟中菜鸟的python学习经验，不求与大牛产生共鸣，但求学习一步一个脚印。还请各位牛人不吝赐教。

近期尝试安装myqr模块，终端输入pip3 install myqr 一切顺利，但最后给出了pip版本过低的提示：
然后按照提示，输入pip install --upgrade pip, 各种提示“Command not found",最后通过万能的搜索引擎，搜索到了正确的命令：pip3 install --upgrade pip

 大功告成！

 详细日志贴上一波如下:

ai-nixs:~ nixinsheng$ pip3 install --upgrade pip
Requirement already satisfied: pip in /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (21.0.1)
You have new mail in /var/mail/nixinsheng
ai-nixs:~ nixinsheng$ pip --version
pip 21.0.1 from /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/pip (python 3.6)
ai-nixs:~ nixinsheng$ pip install pyinstaller
Collecting pyinstaller
  Downloading pyinstaller-4.2.tar.gz (3.6 MB)
     |████████████████████████████████| 3.6 MB 11 kB/s
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
    Preparing wheel metadata ... done
Collecting pyinstaller-hooks-contrib>=2020.6
  Downloading pyinstaller_hooks_contrib-2020.11-py2.py3-none-any.whl (172 kB)
     |████████████████████████████████| 172 kB 8.5 kB/s
Requirement already satisfied: setuptools in /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (from pyinstaller) (39.0.1)
Collecting altgraph
  Downloading altgraph-0.17-py2.py3-none-any.whl (21 kB)
Collecting macholib>=1.8
  Downloading macholib-1.14-py2.py3-none-any.whl (37 kB)
Collecting importlib-metadata
  Downloading importlib_metadata-3.4.0-py3-none-any.whl (10 kB)
Collecting zipp>=0.5
  Downloading zipp-3.4.0-py3-none-any.whl (5.2 kB)
Collecting typing-extensions>=3.6.4
  Downloading typing_extensions-3.7.4.3-py3-none-any.whl (22 kB)
Building wheels for collected packages: pyinstaller
  Building wheel for pyinstaller (PEP 517) ... done
  Created wheel for pyinstaller: filename=pyinstaller-4.2-py3-none-any.whl size=2413076 sha256=d4e8d768b8ec7b313c648ad7f611019321d6d1d64eb4195c505267ba4ec45a6c
  Stored in directory: /Users/nixinsheng/Library/Caches/pip/wheels/b1/17/ed/959da2734eb4be7742242a2042ed6c77a6ba812f45623b6c56
Successfully built pyinstaller
Installing collected packages: zipp, typing-extensions, altgraph, pyinstaller-hooks-contrib, macholib, importlib-metadata, pyinstaller
Successfully installed altgraph-0.17 importlib-metadata-3.4.0 macholib-1.14 pyinstaller-4.2 pyinstaller-hooks-contrib-2020.11 typing-extensions-3.7.4.3 zipp-3.4.0
You have new mail in /var/mail/nixinsheng
ai-nixs:~ nixinsheng$