invoice = """
0.....6.................................40........52...55........
1909  Pimoroni PiBrella                     $17.50    3    $52.50
1489  6mm Tactile Switch x20                 $4.95    2     $9.90
1510  Panavise Jr. - PV-201                 $28.00    1    $28.00
1601  PiTFT Mini Kit 320x240                $34.95    1    $34.95
"""

structure = dict(
    SKU = slice(0, 6),
    DESCRIPTION = slice(6, 40),
    UNIT_PRICE = slice(40, 52),
    QUANTITY =  slice(52, 55),
    ITEM_TOTAL = slice(55, None),
)

for line in invoice.split('\n')[2:]:
    line_item = {}
    for field, chunk in structure.items():
        line_item[field] = line[chunk].strip()
    print(line_item)