Script to set all layers to fixed LSB & RSB

This is my first script so excuse my derp. This is what I tried:

for thisGlyph in Glyphs.font.selectedLayers:
	thisGlyph.RSB = 30
	thisGlyph.LSB = 30

And that works, but how can I make it do all the layers in the glyph?

Actually you only set new RSB and LSB for selected layers.
If you want to this for all layer of a glyph you need :

for layer in Glyphs.font.selectedLayers:
    # Access to the glyph 
    glyph = layer.parent
    # Access to all layer of the glyph
    for layer in glyph.layers:
	      layer.RSB = 30
	      layer.LSB = 30

I know, hence the reason for my question. But thank you, your code is exactly what I needed.

Or set the metrics keys:

for sl in Font.selectedLayers:
	g = sl.parent
	g.leftMetricsKey = "=30"
	g.rightMetricsKey = "=30"
	for l in g.layers:

Or set the =30 on one glyph and add =glyphname to all other glyphs (replace glyphname with the name of the first glyph).

Also a good idea.