CadQuery simple L-shaped piece example (with STEP export)

import cadquery as cq

# Define dimensions
base_length = 200  # 20cm
base_width = 80    # 8cm
plate_thickness = 2  # 2mm
upright_height = 400  # 40cm

# Create the base plate
base_plate = cq.Workplane("XY").box(base_length, base_width, plate_thickness)

# Create the upright plate
# Position is set such that it aligns with the end of the base plate and stands upright
upright_plate = cq.Workplane("XY").workplane(offset=plate_thickness).transformed(rotate=(0, 90, 0)).box(upright_height, base_width, plate_thickness).translate((base_length/2, 0, upright_height/2))

# Join the two parts into one
final_part = base_plate.union(upright_plate)

# Export to STEP
final_part.val().exportStep("L-piece.stp")