初学 Python 在使用 pip3 安装依赖时报错

Traceback (most recent call last):
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pkg_resources/__init__.py", line 583, in _build_master
    ws.require(__requires__)
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pkg_resources/__init__.py", line 900, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pkg_resources/__init__.py", line 791, in resolve
    raise VersionConflict(dist, req).with_context(dependent_req)
pkg_resources.VersionConflict: (pip 21.1.2 (/Users/wangjiaxin/Library/Python/3.8/lib/python/site-packages), Requirement.parse('pip==20.3.1'))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/bin/pip3", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pkg_resources/__init__.py", line 3251, in <module>
    def _initialize_master_working_set():
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pkg_resources/__init__.py", line 3234, in _call_aside
    f(*args, **kwargs)
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pkg_resources/__init__.py", line 3263, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pkg_resources/__init__.py", line 585, in _build_master
    return cls._build_from_requirements(__requires__)
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pkg_resources/__init__.py", line 598, in _build_from_requirements
    dists = ws.resolve(reqs, Environment())
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pkg_resources/__init__.py", line 786, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'pip==20.3.1' distribution was not found and is required by the application

直接使用 pip 没问题, 但是依赖包会安装到 Python2.x 下
使用 python3 -m pip 命令正常, 怀疑 pip3 命令配置有问题, 接着使用 python -m pip -V 查看 Python3 下对应的 pip 版本, 果然输出结果跟报错中提示的版本不同

$ python3 -m pip -V     
pip 21.1.2

是不是只要修改 pip3 中的版本号就可以了?
通过 which pip3 找到 pip3 所在目录, 打开替换其中的版本号 20.3.1 为上面输出的 '21.1.2'

#!/usr/bin/python3
# EASY-INSTALL-ENTRY-SCRIPT: 'pip==21.1.2','console_scripts','pip3'
__requires__ = 'pip==21.1.2'
import re
import sys
from pkg_resources import load_entry_point

if __name__ == '__main__':
    sys.argv[0] = re.sub(r'(-script\.pyw?|\.exe)?$', '', sys.argv[0])
    sys.exit(
        load_entry_point('pip==21.1.2', 'console_scripts', 'pip3')()
    )

保存 重新执行 pip3 完美!