I ran into this same issue on Windows 10. Here's how I fixed it:

1. Open your 'Environment Variables' (Under 'System Properties').
2. In the window that opens, select the 'Path' row, then click the 'Edit...' button.
3. There should be two environment variables C:\Python37-32\Scripts\ and C:\Python37-32\ Then click 'OK' (Make sure to check that these path values correspond to the location and version of your Python install.)
4. Next, in the top portion of the 'Environment Variables' window, look for the PYTHONHOME variable and make sure that it is also set to C:\Python37-32

This issue has been addressed here in this thread. Apparently, running the Python setup as an administrator and/or correctly setting the environment variables solved this issue.

First, don't forget to select "Add Python 3.x to PATH" before you click on Install now and reboot after installation so that the new path is taken into account by Windows.

Second, I had the the same problem with Python 3 on Windows 7 and 64-bit and I got rid of it by deleting PYTHONPATH and PYTHONHOME from Windows 7 system environment variables, because I had a previous installation of Python 2 and those paths were pointing to my the Python 2 directory. I had to simply to delete the PYTHONPATH and PYTHONHOME variables.