code: def set_extent_size(self, length, units):
          
          size = length * size_units[units]
          self.open()
          ext = lvm_vg_set_extent_size(self.handle, c_ulong(size))
          self._commit()
          self.close()
          if ext != 0:
              raise CommitError("Failed to set extent size.")
docs: Sets the volume group extent size in the given units::
  
              from lvm2py import *
  
              lvm = LVM()
              vg = lvm.get_vg("myvg", "w")
              vg.set_extent_size(2, "MiB")
  
          *Args:*
  
          *       length (int):   The desired length size.
          *       units (str):    The desired units ("MiB", "GiB", etc...).
  
          *Raises:*
  
          *       HandleError,  CommitError, KeyError
  
          .. note::
  
              The VolumeGroup instance must be in write mode, otherwise CommitError
              is raised.