pip install access denied on Windows

Change your Python installation folder's security permissions by:

1. Open a Python shell
2. Go to task manager
3. Find the python process
4. Right-click and open location
5. The folder will open in explorer, go up a directory
6. Right-click the folder and select properties
7. Click the security tab and hit 'edit'
8. Add everyone and give them permission to Read and Write.
9. Save your changes

If you open cmd as admin; then you can do the following:

If Python is set in your PATH, then:

python -m pip install mitmproxy

For Windows, in Command Prompt (Admin) try to run pip install using the Python executable:

python -m pip install mitmproxy

This should work, at least it worked for me for other package installation.