How to use the mistune.block_parser.expand_leading_tab function in mistune

def preprocess(s, state):
    state.update({
        'def_links': {},
        'def_footnotes': {},
        'footnotes': [],
    })

    if s is None:
        s = '\n'
    else:
        s = s.replace('\u2424', '\n')
        s = _newline_pattern.sub('\n', s)
        s = _blank_lines.sub('', s)
        s = expand_leading_tab(s)
        if not s.endswith('\n'):
            s += '\n'

    return s, state