Connecting psycopg2 to dockerized postgreSQL

Question

I am trying to connect to a postgreQSL-database initialized within a Dockerized Django project. I am currently using the python package psycopg2 inside a Notebook in Jupyter to connect and add/manipulate data inside the db.

With the code:

connector = psycopg2 .connect(
    database="postgres",
    user="postgres",
    password="postgres",
    host="postgres",
    port="5432")

It raises the following error:

OperationalError: could not translate host name "postgres" to address: Unknown host

Meanwhile, It connects correctly to the local db named postgres with host as localhost or 127.0.0.1, but it is not the db I want to access. How can I connect from Python to the db? Should I change something in the project setup?

You can find the Github repository here. Many thanks!

docker-compose.yml:

version: '3.8'

services:
  web:
    restart: always
    build: ./web
    expose:
      - "8000"
    links:
      - postgres:postgres
      - redis:redis
    volumes:
      - web-django:/usr/src/app
      - web-static:/usr/src/app/static
    env_file: .env
    environment:
      DEBUG: 'true'
    command: /usr/local/bin/gunicorn docker_django.wsgi:application -w 2 -b :8000

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

  postgres:
    restart: always
    image: postgres:latest
    hostname: postgres
    ports:
      - "5432:5432"
    volumes:
      - pgdata:/var/lib/postgresql/data/
    environment:
      POSTGRES_DB: postgres
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres

  pgadmin:
    image: dpage/pgadmin4
    depends_on:
      - postgres
    ports:
      - "5050:80"
    environment:
      PGADMIN_DEFAULT_EMAIL: pgadmin4@pgadmin.org
      PGADMIN_DEFAULT_PASSWORD: admin
    restart: unless-stopped

  redis:
    restart: always
    image: redis:latest
    ports:
      - "6379:6379"
    volumes:
      - redisdata:/data

volumes:
  web-django:
  web-static:
  pgdata:
  redisdata:

Dockefile:

FROM python:3.7-slim

RUN python -m pip install --upgrade pip

COPY requirements.txt requirements.txt
RUN python -m pip install -r requirements.txt

COPY . .

Edit

To verify that localhost is not the correct hostname I tried to visualize the tables inside PgAdmin (which connects to the correct host), and psycopg2:

The (correct) tables of pgadmin:

The (incorrect) tables of psycopg2: