Example 1: 

Add a multi-term model (image.model from clean) to an MS ('myMS.ms'), spectral window 3, writing directly to the MODEL column:

ft(vis='myMS.ms', spw=3, nterms=2, model=['image.model.tt0','image.model.tt1'], usescratch=True) 


Example 2: 

Create a component list with a point source at position J2000 12h33m45.3s -23d01m11.2s with a spectral index of -0.8 and a flux of 13.4 Jy at a reference frequency of 1.25GHz; insert it into 'myMS.ms' as a virtual model for field 3:

#first create the component list
cl.addcomponent(shape='point', flux='13.4Jy', spectrum type='spectral index', index=-0.8, freq'1.25GHz', dir='J2000 12h33m45.3s -23d01m11.2s')
# save the component list under the name 'mycomplist.cl'
#now insert the component list into myMS.ms as a virtual MODEL
ft(vis='myMS.ms', field='3', complist='mycomplist.cl', usescratch=True)