How to use the cairosvg.helpers.normalize function in CairoSVG

def bounding_box_path(surface, node):
    """Get the bounding box of a ``path`` node."""
    path_data = node.get('d', '')

    # Normalize path data for correct parsing
    for letter in PATH_LETTERS:
        path_data = path_data.replace(letter, ' {} '.format(letter))
    path_data = normalize(path_data)

    bounding_box = EMPTY_BOUNDING_BOX
    previous_x = 0
    previous_y = 0
    letter = 'M'    # Move as default
    while path_data:
        path_data = path_data.strip()
        if path_data.split(' ', 1)[0] in PATH_LETTERS:
            letter, path_data = (path_data + ' ').split(' ', 1)

        if letter in 'aA':
            # Elliptical arc curve
            rx, ry, path_data = point(None, path_data)
            rotation, path_data = path_data.split(' ', 1)
            rotation = radians(float(rotation))

size(self, node.get('y'), 'y'))

        # Set node's drawing informations if the ``node.tag`` method exists
        line_cap = node.get('stroke-linecap')
        if line_cap == 'square':
            self.context.set_line_cap(cairo.LINE_CAP_SQUARE)
        if line_cap == 'round':
            self.context.set_line_cap(cairo.LINE_CAP_ROUND)

        join_cap = node.get('stroke-linejoin')
        if join_cap == 'round':
            self.context.set_line_join(cairo.LINE_JOIN_ROUND)
        if join_cap == 'bevel':
            self.context.set_line_join(cairo.LINE_JOIN_BEVEL)

        dash_array = normalize(node.get('stroke-dasharray', '')).split()
        if dash_array:
            dashes = [size(self, dash) for dash in dash_array]
            if sum(dashes):
                offset = size(self, node.get('stroke-dashoffset'))
                self.context.set_dash(dashes, offset)

        miter_limit = float(node.get('stroke-miterlimit', 4))
        self.context.set_miter_limit(miter_limit)

        # Clip
        rect_values = clip_rect(node.get('clip'))
        if len(rect_values) == 4:
            top = size(self, rect_values[0], 'y')
            right = size(self, rect_values[1], 'x')
            bottom = size(self, rect_values[2], 'y')
            left = size(self, rect_values[3], 'x')

def path(surface, node):
    """Draw a path ``node``."""
    string = node.get('d', '')

    node.vertices = []

    for letter in PATH_LETTERS:
        string = string.replace(letter, ' {} '.format(letter))

    last_letter = None
    string = normalize(string)

    # Keep the current point because Cairo's get_current_point is not accurate
    # enough. See https://github.com/Kozea/CairoSVG/issues/111.
    if surface.context.has_current_point():
        current_point = surface.context.get_current_point()
    else:
        surface.context.move_to(0, 0)
        current_point = 0, 0

    while string:
        string = string.strip()
        if string.split(' ', 1)[0] in PATH_LETTERS:
            letter, string = (string + ' ').split(' ', 1)
            if last_letter in (None, 'z', 'Z') and letter not in 'mM':
                node.vertices.append(current_point)
                first_path_point = current_point

x, y, dx, dy, rotate = [], [], [], [], [0]
    if 'x' in node:
        x = [size(surface, i, 'x')
             for i in normalize(node['x']).strip().split(' ')]
    if 'y' in node:
        y = [size(surface, i, 'y')
             for i in normalize(node['y']).strip().split(' ')]
    if 'dx' in node:
        dx = [size(surface, i, 'x')
              for i in normalize(node['dx']).strip().split(' ')]
    if 'dy' in node:
        dy = [size(surface, i, 'y')
              for i in normalize(node['dy']).strip().split(' ')]
    if 'rotate' in node:
        rotate = [radians(float(i)) if i else 0
                  for i in normalize(node['rotate']).strip().split(' ')]
    last_r = rotate[-1]
    letters_positions = zip_letters(x, y, dx, dy, rotate, node.text)

    x_align = 0
    y_align = 0

    text_anchor = node.get('text-anchor')
    if text_anchor == 'middle':
        x_align = width / 2. + x_bearing
    elif text_anchor == 'end':
        x_align = width + x_bearing

    # TODO: This is a hack. The rest of the baseline alignment tags of the SVG
    # 1.1 spec (section 10.9.2) are not supported. We only try to align things
    # that look like Western horizontal fonts.
    # Finally, we add a "display-anchor" attribute for aligning the specific

def polyline(surface, node):
    """Draw a polyline ``node``."""
    points = normalize(node.get('points', ''))
    if points:
        x, y, points = point(surface, points)
        surface.context.move_to(x, y)
        node.vertices = [(x, y)]
        while points:
            x_old, y_old = x, y
            x, y, points = point(surface, points)
            angle = point_angle(x_old, y_old, x, y)
            node.vertices.append((pi - angle, angle))
            surface.context.line_to(x, y)
            node.vertices.append((x, y))

def bounding_box_polyline(surface, node):
    """Get the bounding box of a ``polyline`` or ``polygon`` node."""
    bounding_box = EMPTY_BOUNDING_BOX
    points = []
    normalized_points = normalize(node.get('points', ''))
    while normalized_points:
        x, y, normalized_points = point(surface, normalized_points)
        points.append((x, y))
    return extend_bounding_box(bounding_box, points)