caltable: the name of the gencal-produced Tsys cal table to correct
sqld: the path to the SysCal.xml file to get the SQLD Tsys values from
asdm: the path to the original ASDM (with SpectralWindow.xml and Scan.xml)
spws: the spws to replace (in order of baseband number). It can be either a python list of integers, or a comma-delimited string of integers. The number of spws specified must match the number of SQLDs in the SysCal.xml file.