A simple table of contents using ReportLab (does not work!)

simple_toc.py

from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.platypus import SimpleDocTemplate, Paragraph
from reportlab.platypus import PageBreak
from reportlab.platypus.tableofcontents import TableOfContents


def simple_toc():
    doc = SimpleDocTemplate("simple_toc.pdf")
    story = []
    styles = getSampleStyleSheet()

    toc = TableOfContents()
    toc.levelStyles = [
        ParagraphStyle(fontName='Helvetica', fontSize=14, name='Heading1',
                       leftIndent=20, firstLineIndent=-20, spaceBefore=5,
                       leading=16),
        ParagraphStyle(fontName='Times-Roman', fontSize=14, name='Heading2',
                           leftIndent=20, firstLineIndent=-20, spaceBefore=5,
                           leading=16),
    ]
    story.append(toc)

    ipsum = '''Lorem ipsum dolor sit amet, consectetur adipiscing elit,
    sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
    Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris
    nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in
    reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla
    pariatur. Excepteur sint occaecat cupidatat non proident, sunt in
    culpa qui officia deserunt mollit anim id est laborum.'''

    para = Paragraph("The Beginning", style=styles['Heading1'])
    toc.addEntry(0, 'The Beginning', 1)
    story.append(para)
    para = Paragraph(ipsum, style=styles['Normal'])
    story.append(para)
    story.append(PageBreak())

    para = Paragraph("The Middle", style=styles['Heading1'])
    toc.addEntry(0, 'The Middle', 2)
    story.append(para)
    para = Paragraph("The Middle Sub-Header", style=styles['Heading2'])
    toc.addEntry(1, 'The Middle Sub-Header', 2)
    story.append(para)
    para = Paragraph(ipsum, style=styles['Normal'])
    story.append(para)
    story.append(PageBreak())

    para = Paragraph("The End", style=styles['Heading1'])
    toc.addEntry(0, 'The End', 3)
    story.append(para)

    doc.multiBuild(story)

if __name__ == '__main__':
    simple_toc()