What is the correct way to add repo via artifactory to install nginx in python:2.7.18-slim?

Question

linux

In general, I need a lightweight image python on version 2.7, since I need to raise the nginx version and leave legacy python
on 2.7 for now .

Found python: 2.7.18-slim-stretch

external repo for debian
.

FROM python:2.7.18-slim

ENV TZ=Europe/Moscow
RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone


RUN rm /etc/apt/sources.list \
  && echo 'deb http://rero.ru/artifactory/debian-remote stretch main' >> /etc/apt/sources.list \
  && echo 'deb http://rero.ru/artifactory/debian-remote stretch-updates main' >> /etc/apt/sources.list \
  && echo 'deb http://rero.ru/artifactory/debian-security stretch/updates main' >> /etc/apt/sources.list \
  && apt-get update \
  && apt-get install nginx

run build

returns error

#6 6.543 The following packages have unmet dependencies:
#6 6.595  nginx : Depends: nginx-full (< 1.10.3-1+deb9u7.1~) but it is not going to be installed or
#6 6.595                   nginx-light (< 1.10.3-1+deb9u7.1~) but it is not going to be installed or
#6 6.595                   nginx-extras (< 1.10.3-1+deb9u7.1~) but it is not going to be installed
#6 6.595          Depends: nginx-full (>= 1.10.3-1+deb9u7) but it is not going to be installed or
#6 6.595                   nginx-light (>= 1.10.3-1+deb9u7) but it is not going to be installed or
#6 6.595                   nginx-extras (>= 1.10.3-1+deb9u7) but it is not going to be installed
#6 6.606 E: Unable to correct problems, you have held broken packages.

what repo or dependency is missing?