I have met same issue when I install Python, and it is resolved when I set a PATH in system, here are the steps.
- Navigate to "Control Panel" -> "System"
- Click "Advanced system settings" on the left
- Click "Environment Variables"
- Search and click "Path" variable
- Click "Edit"
- Add "C:\"to the environment variables field, if you are using Windows7, then separate it by a semicolon from the existing entry. If you are using Windows10, just simply click "New" to add.
- Reopen the Command Prompt and try
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