add explicit paramter for infinite iterators

set appropriate value for num_epoch param for iteratos

fix long lines

remove trailing whitespace

fixed typo

remove comment

fixed comments

fixed test

Fix error msg of pythontokenizer

add string implementation, can handle partial string slices

finish core implementation, added Index object

fix up the logic

add in new SliceOption object, cleaning up tests

- cleanup work on createTensor and Tensor's constructors