server:/home/script# mountpy /dev/hdc
Mounted /dev/hdc iso9660
List of mounted devices:  /dev/hdc
server:/home/script# umount /dev/hdc
server:/home/script#               

script@server:~$ mountpy /dev/hdc

mountpy is not being run with enough privileges.
There are 3 ways how to make mountpy run comfortably with root privileges:
1) install sudo, add this line to /etc/sudoers:
joesmith ALL = NOPASSWD: /usr/bin/mountpy, usr/bin/umountpy
  to allow user joesmith use mountpy.
  It you want to allow all the users use mountpy, change the line into:
ALL ALL = NOPASSWD: /usr/bin/mountpy, usr/bin/umountpy
  and then run „sudo mountpy” and „sudo umountpy”
2) install super, add these lines to /etc/super.tab:
  mountpy /usr/bin/mountpy.py joesmith
umountpy /usr/bin/umountpy joesmith
  to allow user joesmith to run mountpy, or:
mountpy /usr/bin/mountpy.py .*
umountpy /usr/bin/umountpy .*
  to give access to all the users, and run „super mountpy” or „super umountpy”
3) make the C wrapper script setuid root
  log in as root and type:
chmod u+s /usr/bin/mountpy

Be aware that giving all the users rights to execute mountpy can be a
security risk, if an exploitable bug is found in mountpy.  This is
especially true in the 3rd case. Therefore, it is recommended to allow
only selected users to run mountpy, and use super or sudo if possible.
Press ENTER to try anyway
Traceback (most recent call last):
  File „/usr/bin/mountpy.py”, line 318, in ?
    os.setuid(0)
OSError: [Errno 1] Operation not permitted
script@server:~$