Improve the error message for unsupported python2
MODIFY
repo2docker/buildpacks/python/__init__.py
repo2docker/buildpacks/python/__init__.py
@@ -266,4 +266,10 @@ class Python2BuildPack(PythonBuildPack):
runtime = f.read().strip()
if runtime == 'python-2.7':
return True
+ elif runtime.startswith('python-2'):
+ raise ValueError(
+ "Only python-2.7 or python-3.x is supported in "
+ "runtime.txt, not '{}'".format(runtime_txt))
+ else:
+ return False
return False

Improve the error message for unsupported python2