Python, "subprocess.check_ouput()" hangs while installing rpm -

i trying install .rpm through subprocess.check_ouput() i.e.

buff=subprocess.check_output(["rpm","-ivh","package_name"]) 

even though package installed, python script stuck @ instruction (not executing below instructions.)

please note other "rpm" operation working subprocess.check_output()

after including shell=true, i.e.

buff=subprocess.check_output(["rpm","-ivh","package_name"],shell=true) 

package not getting installed , throwing error @ instruction, error : rpm usage

can help?