interpolation with round=False will correctly produce glyph.width as a float if (and only if) your Snap points setting is zero. (in Preferences > Glyph View > Display)

the RoboFont UI may round glyph widths to integers though – for example, if you edit a glyph width using the Space Center or the Inspector, it will become an integer. so, if you want to keep glyph widths as floats, don’t edit them in the UI.

hope this helps!

1. Is there a way to set and unset that with a script so that I don't have to remember to manually change it?

2. Do I need to set that when using other tools (like DesignSpaceEdit, Skateboard, Batch, etc.) so that they don't round data from an imported UFO?

Really appreciate your help with this!

(1)Is there a way to set and unset that with a script so that I don't have to remember to manually change it?

yes, here’s a quick example:

from mojo.UI import getDefault, setDefault

# store current snap value
snapValue = getDefault('glyphViewRoundValues')
print('snap value was:', snapValue)

# set snap value to zero
print('setting snap value to 0')
setDefault('glyphViewRoundValues', 0)

# do something...

# restore previous value when done
setDefault('glyphViewRoundValues', snapValue)
print('restoring snap value of', snapValue)

(2) Do I need to set that when using other tools (like DesignSpaceEdit, Skateboard, Batch, etc.) so that they don't round data from an imported UFO?

yes. the round value is used by the native glyph object (even without the UI), and when generating fonts.

glyph widths are always rounded to integers when generating fonts, this is a restriction of the OpenType horizontal metrics table (htmx).

hope this helps. good luck!