ROS is performed rosrun rqt_graph given No module named 'rospkg'

Environment: ubuntu18.04 + ROS Melodic
execute the command ros run rqt_graph rqt_graphgiven:

Traceback (most recent call last):
  File "/opt/ros/melodic/lib/rqt_graph/rqt_graph", line 5, in <module>
    from rqt_gui.main import Main
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rqt_gui/main.py", line 38, in <module>
    import rospy
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rospy/__init__.py", line 49, in <module>
    from .client import spin, myargv, init_node, \
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rospy/client.py", line 52, in <module>
    import roslib
  File "/opt/ros/melodic/lib/python2.7/dist-packages/roslib/__init__.py", line 50, in <module>
    from roslib.launcher import load_manifest
  File "/opt/ros/melodic/lib/python2.7/dist-packages/roslib/launcher.py", line 42, in <module>
    import rospkg
ModuleNotFoundError: No module named 'rospkg'

Rospkg installation package:

pip install rospkg

Run again after the completion of the installation ros run rqt_graph rqt_graph, continue being given No module named 'pydot',
installation pydot:

pip install pydot

After successful installation, run ros run rqt_graph rqt_graphafter:

Reference Hirofumi

ROS execution rosrun rqt_graph error No module named 'catkin_pkg'