why function throws an error?

--===============5632353191954025360==
Content-Type: multipart/alternative; boundary="000000000000d9b15105e27d6502"

--000000000000d9b15105e27d6502
Content-Type: text/plain; charset="UTF-8"

        def add_route(self, route):
        #    """ Add a route object, but do not change the :data:`Route.app`
        #        attribute."""
            self.routes.append(route)
            self.router.add(route.rule, route.method, route, name=route.name
)
        #    if DEBUG: route.prepare()
--
<https://netanel.ml>

--000000000000d9b15105e27d6502
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

<div dir=3D"rtl"><div style=3D"direction:ltr"><br></div><div><div style=3D"=
direction:ltr"><br></div><div style=3D"direction:ltr">=C2=A0 =C2=A0 =C2=A0 =
=C2=A0 def add_route(self, route):</div><div style=3D"direction:ltr">=C2=A0=
 =C2=A0 =C2=A0 =C2=A0 # =C2=A0 =C2=A0&quot;&quot;&quot; Add a route object,=
 but do not change the :data:`Route.app`</div><div style=3D"direction:ltr">=
=C2=A0 =C2=A0 =C2=A0 =C2=A0 # =C2=A0 =C2=A0 =C2=A0 =C2=A0attribute.&quot;&q=
uot;&quot;</div><div style=3D"direction:ltr">=C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 self.routes.append(route)</div><div style=3D"direction:ltr">=
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 self.router.add(route.rule, route=
.method, route, name=3D<a href=3D"http://route.name">route.name</a>)</div><=
div style=3D"direction:ltr">=C2=A0 =C2=A0 =C2=A0 =C2=A0 # =C2=A0 =C2=A0if D=
EBUG: route.prepare()</div></div><div style=3D"direction:ltr">--</div><div =
dir=3D"rtl" class=3D"gmail_signature" data-smartmail=3D"gmail_signature"><d=
iv dir=3D"rtl" style=3D"direction:ltr"><a href=3D"https://netanel.ml" targe=
t=3D"_blank"><img width=3D"200" height=3D"51" src=3D"https://ci3.googleuser=
content.com/mail-sig/AIorK4ykFjL1iagUdlm0jcadJlaq1KyDf5c3YeE3nLFugFyn69aRMA=
cHd2OKO51XtKIvhzIdbuX81XE"></a></div></div></div>

--000000000000d9b15105e27d6502--

--===============5632353191954025360==
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: inline