How to use the panflute.tools.debug function in panflute

sys.stdout = alt_stdout = StringIO()

    for filter_, filter_path, module_, extra_dir in filter_paths:
        if verbose:
            debug("panflute: running filter <{}>".format(filter_))
        with ContextImport(module_, extra_dir) as module:
            try:
                module.main(doc)
            except Exception as e:
                debug("Failed to run filter: " + filter_)
                if not hasattr(module, 'main'):
                    debug(' - Possible cause: filter lacks a main() function')
                debug('Filter code:')
                debug('-' * 64)
                with open(filter_path) as fp:
                    debug(fp.read())
                debug('-' * 64)
                raise Exception(e)
        if verbose:
            debug("panflute: filter <{}> completed".format(filter_))
        
        alt_stdout_data = alt_stdout.getvalue()
        if alt_stdout_data:
            debug('[PANFLUTE WARNING] Filter "{}" wrote to stdout, but Pandoc does not allow that'.format(filter_))
            debug(alt_stdout_data)
            sys.stderr.flush()
            sys.stdout = alt_stdout = StringIO()

    # Restore stdout
    sys.stdout = sys.__stdout__

    return doc

debug(msg)

    if filters is None:
        # metadata 'panflute-filters' can be a list, a string, or missing
        # `filters` should be a list of str
        filters = doc.get_metadata('panflute-filters', [])
        if type(filters) != list:
            filters = [filters]

    if filters:
        if verbose:
            msg = "panflute: will run the following filters:"
            debug(msg, ' '.join(filters))
        doc = autorun_filters(filters, doc, search_dirs, verbose)
    elif verbose:
        debug("panflute: no filters were provided")

    dump(doc, output_stream)

elif verbose:
                debug("          filter <{}> NOT found in {}".format(filter_, filter_path))
        else:
            raise Exception("filter not found: " + filter_)

    # Intercept any print() statements made by filters (which would cause Pandoc to fail)
    sys.stdout = alt_stdout = StringIO()

    for filter_, filter_path, module_, extra_dir in filter_paths:
        if verbose:
            debug("panflute: running filter <{}>".format(filter_))
        with ContextImport(module_, extra_dir) as module:
            try:
                module.main(doc)
            except Exception as e:
                debug("Failed to run filter: " + filter_)
                if not hasattr(module, 'main'):
                    debug(' - Possible cause: filter lacks a main() function')
                debug('Filter code:')
                debug('-' * 64)
                with open(filter_path) as fp:
                    debug(fp.read())
                debug('-' * 64)
                raise Exception(e)
        if verbose:
            debug("panflute: filter <{}> completed".format(filter_))
        
        alt_stdout_data = alt_stdout.getvalue()
        if alt_stdout_data:
            debug('[PANFLUTE WARNING] Filter "{}" wrote to stdout, but Pandoc does not allow that'.format(filter_))
            debug(alt_stdout_data)
            sys.stderr.flush()

# Display message (tests that everything is working ok)
    msg = doc.get_metadata('panflute-echo', False)
    if msg:
        debug(msg)

    if filters is None:
        # metadata 'panflute-filters' can be a list, a string, or missing
        # `filters` should be a list of str
        filters = doc.get_metadata('panflute-filters', [])
        if type(filters) != list:
            filters = [filters]

    if filters:
        if verbose:
            msg = "panflute: will run the following filters:"
            debug(msg, ' '.join(filters))
        doc = autorun_filters(filters, doc, search_dirs, verbose)
    elif verbose:
        debug("panflute: no filters were provided")

    dump(doc, output_stream)

if not panfl_:
        # default panflute behaviour:
        search_dirs.append('.')
        if data_dir:
            search_dirs.extend(get_filter_dirs())
        if sys_path:
            search_dirs += sys.path
    else:
        # panfl/pandoctools behaviour:
        if data_dir:
            search_dirs.extend(get_filter_dirs())
        if sys_path:
            search_dirs += reduced_sys_path

    if verbose:
        debug('panflute will search for filters in the following folders:')
        debug(' '.join('"{}"'.format(f) for f in search_dirs))

    # Display message (tests that everything is working ok)
    msg = doc.get_metadata('panflute-echo', False)
    if msg:
        debug(msg)

    if filters is None:
        # metadata 'panflute-filters' can be a list, a string, or missing
        # `filters` should be a list of str
        filters = doc.get_metadata('panflute-filters', [])
        if type(filters) != list:
            filters = [filters]

    if filters:
        if verbose:

else:
            module = False
            # allow with and without .py ending
            path_postfixes = (remove_py(filter_exp) + '.py',)

        for path, path_postf in [(path, path_postf)
                                 for path in search_dirs
                                 for path_postf in path_postfixes]:
            if p.isabs(path_postf):
                filter_path = path_postf
            else:
                filter_path = p.abspath(p.normpath(p.join(path, path_postf)))

            if p.isfile(filter_path):
                if verbose:
                    debug("panflute: filter <{}> found in {}".format(filter_, filter_path))

                if module and not (path in reduced_sys_path):
                    extra_dir = p.abspath(path)
                    # `path` already doesn't contain `.`, `..`, env vars or `~`
                else:
                    extra_dir = None
                module_ = filter_exp if module else filter_path

                filter_paths.append((filter_, filter_path, module_, extra_dir))
                break
            elif p.isabs(path_postf):
                if verbose:
                    debug("          filter <{}> NOT found in {}".format(filter_, filter_path))
                raise Exception("filter not found: " + filter_)
            elif verbose:
                debug("          filter <{}> NOT found in {}".format(filter_, filter_path))

for filter_, filter_path, module_, extra_dir in filter_paths:
        if verbose:
            debug("panflute: running filter <{}>".format(filter_))
        with ContextImport(module_, extra_dir) as module:
            try:
                module.main(doc)
            except Exception as e:
                debug("Failed to run filter: " + filter_)
                if not hasattr(module, 'main'):
                    debug(' - Possible cause: filter lacks a main() function')
                debug('Filter code:')
                debug('-' * 64)
                with open(filter_path) as fp:
                    debug(fp.read())
                debug('-' * 64)
                raise Exception(e)
        if verbose:
            debug("panflute: filter <{}> completed".format(filter_))
        
        alt_stdout_data = alt_stdout.getvalue()
        if alt_stdout_data:
            debug('[PANFLUTE WARNING] Filter "{}" wrote to stdout, but Pandoc does not allow that'.format(filter_))
            debug(alt_stdout_data)
            sys.stderr.flush()
            sys.stdout = alt_stdout = StringIO()

    # Restore stdout
    sys.stdout = sys.__stdout__

    return doc

raise Exception("filter not found: " + filter_)

    # Intercept any print() statements made by filters (which would cause Pandoc to fail)
    sys.stdout = alt_stdout = StringIO()

    for filter_, filter_path, module_, extra_dir in filter_paths:
        if verbose:
            debug("panflute: running filter <{}>".format(filter_))
        with ContextImport(module_, extra_dir) as module:
            try:
                module.main(doc)
            except Exception as e:
                debug("Failed to run filter: " + filter_)
                if not hasattr(module, 'main'):
                    debug(' - Possible cause: filter lacks a main() function')
                debug('Filter code:')
                debug('-' * 64)
                with open(filter_path) as fp:
                    debug(fp.read())
                debug('-' * 64)
                raise Exception(e)
        if verbose:
            debug("panflute: filter <{}> completed".format(filter_))
        
        alt_stdout_data = alt_stdout.getvalue()
        if alt_stdout_data:
            debug('[PANFLUTE WARNING] Filter "{}" wrote to stdout, but Pandoc does not allow that'.format(filter_))
            debug(alt_stdout_data)
            sys.stderr.flush()
            sys.stdout = alt_stdout = StringIO()

    # Restore stdout

debug("Failed to run filter: " + filter_)
                if not hasattr(module, 'main'):
                    debug(' - Possible cause: filter lacks a main() function')
                debug('Filter code:')
                debug('-' * 64)
                with open(filter_path) as fp:
                    debug(fp.read())
                debug('-' * 64)
                raise Exception(e)
        if verbose:
            debug("panflute: filter <{}> completed".format(filter_))
        
        alt_stdout_data = alt_stdout.getvalue()
        if alt_stdout_data:
            debug('[PANFLUTE WARNING] Filter "{}" wrote to stdout, but Pandoc does not allow that'.format(filter_))
            debug(alt_stdout_data)
            sys.stderr.flush()
            sys.stdout = alt_stdout = StringIO()

    # Restore stdout
    sys.stdout = sys.__stdout__

    return doc