facebookresearch/fairseq

Add an option to disable appending eos to the end of each document while preprocessing

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#5,615 opened on May 26, 2025

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enhancementhelp wantedneeds triage

Description

🚀 Feature Request

Add an option to disable appending EOS to the end of each document while preprocessing

Motivation

There are instances where adding EOS is not preferred like when packing data to sequence length.

Pitch

Proposing a change to add an argument to handle this

Contributor guide

Tech stack
pythonpytorch
Domain
machine learning
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
PythonPyTorchfairseq basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Look for where EOS is appended to documents during preprocessing. Typical locations are in fairseq's dictionary construction (e.g., `fairseq/data/dictionary.py`) or in the binarization scripts (e.g., `fairseq cli/preprocess.py`). The solution involves adding a new argument (e.g., ` no append eos`) to the relevant preprocessing function or CLI tool and conditionally skipping the addition of EOS tokens.