Please help!

roslaunch turtlebot_bringup minimal.launch --screen

... logging to /home/ahmed/.ros/log/7230a1cc-2af0-11e6-8726-74e543e0ae3e/roslaunch-ahmed-HP-ENVY-dv7-Notebook-PC-5114.log Checking log directory for disk usage. This may take awhile. Press Ctrl-C to interrupt Done checking log file disk usage. Usage is <1GB.

Traceback (most recent call last):
File "/opt/ros/indigo/share/xacro/xacro.py", line 60, in import xacro File "/opt/ros/indigo/lib/python2.7/dist-packages/xacro/init.py", line 45, in from roslaunch import substitutionargs File "/opt/ros/indigo/lib/python2.7/dist-packages/roslaunch/init.py", line 48, in import rospkg ImportError: No module named rospkg while processing /opt/ros/indigo/share/turtlebotbringup/launch/includes/robot.launch.xml: while processing /opt/ros/indigo/share/turtlebotbringup/launch/includes/description.launch.xml: Invalid tag: Cannot load command parameter [robotdescription]: command [/opt/ros/indigo/share/xacro/xacro.py '/opt/ros/indigo/share/turtlebotdescription/robots/kobukihexagonsasusxtion_pro.urdf.xacro'] returned with code [1].

Param xml is The traceback for the exception was written to the log file