How to log information of a docker container

Question

I have a docker-compose.yml file that has 3 services 1) nginx : reverse-proxy 2) web : a simple application that takes performs classification using ridge classifier 3) viz : presents statistics of docker information, like CPU used, number of containers used

Below is my docker-compose.yml

version: '2'

services:
  web:
    restart: always
    build: ./web
    expose:
      - "8000"
    volumes:
      - ./output:/usr/src/app/static
    command: /usr/local/bin/gunicorn -w 2 -b :8000 --access-logfile - classifierv2RestEndPoint_ridge_NB:create_app()

  nginx:
    restart: always
    build: ./nginx/
    ports:
      - "80:80"
    volumes:
      - /www/static
    volumes_from:
      - web
    links:
      - web:web

  viz:
    image: dockersamples/visualizer
    ports:
      - 8080:8080/tcp
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    environment:
      - "constraint=node.role==manager"

In 'web' service I have a simple UI that takes a an excel file as input and upon clicking submit button it outputs the result of classifier.

if I incorrectly select a wrong file and click submit it throws an error

However when I check the docker-compose logs, I do not see why the error is happening. I see this

I want to see where in the program is the error happening but not HTTP POST request log

web_1    | 172.19.0.4 - - [10/Sep/2017:17:41:07 +0000] "POST / HTTP/1.0" 500 291 "http                                                          ://ec2-35-154-66-136.ap-south-1.compute.amazonaws.com/" "Mozilla/5.0 (Windows NT 10.0;                                                           Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.113 Safari/537.36    

What should I do to see the error in my classifier code?

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