def generate_nav(self, fun=None):
        self.value_cache += '<p>'
        if fun is None:
            self.value_cache += '<img src="/nbextensions/iprofiler/home.png">'
        else:
            self.value_cache += ('<a id="iprofile_home" '
                                 'style="cursor:pointer">'
                                 '<img src="/nbextensions/iprofiler/home.png">'
                                 '</a>')
        if len(self.backward) > 1:
            self.value_cache += ('<a id="iprofile_back" '
                                 'style="cursor:pointer">'
                                 '<img src="/nbextensions/iprofiler/back.png">'
                                 '</a>')
        else:
            self.value_cache += ('<img src="/nbextensions/iprofiler/back_'
                                 'grey.png">')
        if len(self.forward) > 0:
            self.value_cache += ('<a id="iprofile_forward" '
                                 'style="cursor:pointer"><img' 'src="/nbextensions/iprofiler/forward.png">'
                                 '</a></p>')
        else:
            self.value_cache += ('<img src="/nbextensions/iprofiler/forward_'
                                 'grey.png"></p>')
dataset/ETHPy150Open j-towns/iprofiler/iprofiler.py/IProfile.generate_nav/original