I'm not sure I'm answering the question you asked, but if you want to know which document corresponds to the identifier perhaps the identifiers is just an integer sequence?

So the document with id 0 is the first document in the array of documents that you fed to the vectorizer on line 37?

https://gist.github.com/edsu/6158b975fb3754f0fae3080e7bb66e29#file-topic-model-py-L37

//Ed