How to use the pdfplumber.utils.to_list function in pdfplumber

def draw_vlines(self, locations, **kwargs):
        for x in utils.to_list(locations):
            self.draw_vline(x, **kwargs)
        return self

def draw_lines(self, list_of_lines, **kwargs):
        for x in utils.to_list(list_of_lines):
            self.draw_line(x, **kwargs)
        return self

def draw_rects(self, list_of_rects, **kwargs):
        for x in utils.to_list(list_of_rects):
            self.draw_rect(x, **kwargs)
        return self

def draw_circles(self, list_of_circles, **kwargs):
        for x in utils.to_list(list_of_circles):
            self.draw_circle(x, **kwargs)
        return self