Please include c:\python27\Scripts in SYSTEM PATH
Procedure to add c:\python27\Scripts to system path:
- From the desktop, right click the Computer icon.
- Choose Properties from the context menu.
- Click the Advanced system settings link.
- Click Environment Variables. In the Edit System Variable (or New System Variable) window, add c:\python27\Scripts to the value of the PATH environment variable.(don't delete the existing ones)
Assumption: hoping your installation drive is C
Once you have added it, please close all command prompts and open a new command prompt and try it
Or in a new command prompt, type below command
C:\Python27\Scripts\pip.exe install twilio
EDIT:
If everything fails, try the below way:
Open command prompt, type "python -m pip install twilio" (without quotes).