Im trying to write a python file on my raspberry pi to mute or change the volume of the speaker output when its run. If i type: amixer sset 'Master' 50% in to terminal, the volume is increased by 50% however if i make a python file called filename.py will the following lines:

import os
os.system(amixer sset 'Master' 50%)

and run it in terminal with

sudo python filename.py

it comes up with an error

amixer: Unable to find simple control 'Master',0

How can I just run exactly the same command in terminal as I do in python?