How to get size of a vm througt python sdk?

environment : rhev 3.3
plateform : python sdk api
information search : size of the vm

Hi,
I work with the sdk api in python, I want to know the disk size of the vm, someone help me?
I work with this command :
disk = params.Disk(vm)
print "size of the vm" % (disk.get_size)

The result of the print is the value of "params.Disk(vm)" and not the get_size of the vm.
For exemple the result is : >

I want to keep the size of all the disks used by the virtual machine.
Thanks for your help

Emeline Vales