title: cannot import name 'PackageFinder' from 'pip._internal.index' pip3
body: <p>On my mac, pip3 exists in /usr/bin. When I try to install any package using pip3, it is failing. Even simple 'pip3' also failing with below error.</p>
  <pre><code>Traceback (most recent call last):
    File &quot;/Library/Developer/CommandLineTools/usr/bin/pip3&quot;, line 6, in &lt;module&gt;
      from pip._internal import main
    File &quot;/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pip/_internal/__init__.py&quot;, line 40, in &lt;module&gt;
      from pip._internal.cli.autocompletion import autocomplete
    File &quot;/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pip/_internal/cli/autocompletion.py&quot;, line 8, in &lt;module&gt;
      from pip._internal.cli.main_parser import create_main_parser
    File &quot;/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pip/_internal/cli/main_parser.py&quot;, line 11, in &lt;module&gt;
      from pip._internal.commands import (
    File &quot;/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pip/_internal/commands/__init__.py&quot;, line 6, in &lt;module&gt;
      from pip._internal.commands.completion import CompletionCommand
    File &quot;/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pip/_internal/commands/completion.py&quot;, line 6, in &lt;module&gt;
      from pip._internal.cli.base_command import Command
    File &quot;/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pip/_internal/cli/base_command.py&quot;, line 26, in &lt;module&gt;
      from pip._internal.index import PackageFinder
  ImportError: cannot import name 'PackageFinder' from 'pip._internal.index' (/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/site-packages/pip/_internal/index/__init__.py)
  </code></pre>
  <p>I tried to remove /usr/bin/pip3. But it is saying operation is not permitted. I am unable to remove pip3. Can any one please let me know how to fix this issue.</p>
  <p><strong>Note: I went through some stack overflow questions related to this. Most of the answers suggested to uninstall and install pip3. But I am unable to remove pip3.</strong></p>