Is it possible to use the antlr4 python runtime with python 2.6 or is the minimun required version python 2.7?  I want to use it on CentOS 6.3 that comes with python 2.6.6. If it is not possible, is it known what features of python 2.7 that is used?
The example you used was badly written. input is the name of a built-in Python function. Give the Lexer a FileStream and it might work.
use antlr4 python runtime with python 2.6