UI design: combobox or radiobuttons?

[Rich Shepard]

My applications use environmental data, each of which has to specify the
units (e.g., cm, m, km, ft, yd, mi). With the widget sets I've used
(wxPython and TKinter) I've always used a combobox with the acceptable
choices in it. I'm now planning a new application using PyQt5 and it occured
to me that a set of radio buttons would also work.

While a set of radiobuttons occupies more room on the parent widget than
does a combobox are there any technical or user issues that would suggest
using one over the other?

TIA,

Rich