Python >= 3.7 only.

.travis.yml

 # ref: https://docs.travis-ci.com/user/languages/python
 language: python
 python:
-  - "2.7"
-  - "3.2"
-  - "3.3"
-  - "3.4"
-  - "3.5"
-  #- "3.5-dev" # 3.5 development branch
-  #- "nightly" # points to the latest development branch e.g. 3.6-dev
+  - "3.7"
 # command to install dependencies
 install: "pip install -r requirements.txt"
 # command to run tests

Dockerfile

-FROM python:2-alpine
+FROM python:3.7-alpine
 
 RUN mkdir -p /usr/src/app
 WORKDIR /usr/src/app

tox.ini

 [tox]
-envlist = py27, py35
+envlist = py37
 
 [testenv]
 deps=-r{toxinidir}/requirements.txt