From 6d496eee9145fb38eb9138b211c90704328f09cb Mon Sep 17 00:00:00 2001
From: Nokome Bentley <nokome@stenci.la>
Date: Fri, 16 Nov 2018 11:37:30 +1300
Subject: [PATCH] Ensure Python3 before reading README with encoding arg

If you accidently try to install using Python 2 you get the error

    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/home/nokome/nokome/repo2docker/setup.py", line 5, in <module>
        with open('README.md', encoding="utf8") as f:
    TypeError: 'encoding' is an invalid keyword argument for this function

Ideally the user would be aked to use Python 3 as `python_requires` tells us,
but which isn't reached yet.
This implements that behaviour.
---
 setup.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/setup.py b/setup.py
index 2608529f..f46b17b5 100644
--- a/setup.py
+++ b/setup.py
@@ -1,6 +1,10 @@
 from setuptools import setup, find_packages
 import versioneer
 
+import sys
+if sys.version_info[0] < 3:
+    sys.stderr.write('jupyter-repo2docker requires Python 3 but the running Python is %s.%s.%s' % sys.version_info[:3])
+    sys.exit(1)
 
 with open('README.md', encoding="utf8") as f:
     readme = f.read()