tiff_set example

Could you please provide tiff_set function example?
I did several tries and looked into src code, but nothing seems to work for me.
For starters I tried to save F_Num exif data like so (my input tiff has no exif at all):

`tifftools.tiff_set(	source=tiff, output=tiff_new, overwrite=True, setlist=[
		( "33437:RATIONAL", '56 10')
	] )`