I just tried for the first time to set paperformat='letter', and
discovered an error. in _paperformats, the units for 'letter'
and 'legal' are specified as
"letter" : ("8.5 t in", "11 t in"),
"legal" : ("8.5 t in", "14 t in")}
unfortunately, pyx.units defines the inch unit as 'inch' and
not 'in'. Please either add 'in' as an alias for an inch in
pyx.units, or change _paperformats in pyx.canvas to use the