Your first script

Step 1: Open the Scripting window

Choose Scripts › Scripting window.

• Python scripting →

Step 2: Select some glyphs

In the glyph grid, select a few glyphs whose spacing you want to set.

• The glyph grid →

Step 3: Write the script

Replace the text in the editor with this.

for glyph in CurrentFont().selectedGlyphs:
    glyph.leftMargin = 40
    glyph.rightMargin = 40

Step 4: Run it

Press Ctrl+Enter. The selected glyphs now have 40 units on each side.

• Python scripting →

Step 5: Undo it

Press Ctrl+Z in the main window: the whole run undoes in one step.

• Undo →