<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add_image(self, image_path, width=None, height=None, section=None):
 """Add an image to the document. Images are shown on the final document in the order they are added, either within the given section or as part of the un-sectioned list of content. Parameters image_path : str A path to the image on the local file system. width : int or float The width of the image in the document in inches. height : int or float The height of the image in the document in incehs. section : str (This must be a keyword) Select a section in which to place this image. Default is None, in which case the image will be simply be added to a default list of text and images. """

        if width is not None:
            width = width*inch
        if height is not None:
            height = height*inch
        im = Image(image_path, width, height)
        if section is None:
            self.story.append(im)
        else:
            self.sections[section].append(im)
        return