[QUESTION] Confusion about return if args.partitions==1

[qazwsx74269]

When I want to preprocess data for pretraining Bert model, I find this code snippet,

python tools/preprocess_data.py \
       --input my-corpus.json \
       --output-prefix my-bert \
       --vocab-file bert-vocab.txt \
       --tokenizer-type BertWordPieceLowerCase \
       --split-sentences

does not work. It won't generate .bin and .idx files because return after if args.partitions==1 ends the program.

Megatron-LM/tools/preprocess_data.py

Line 362 in 86e2927

return

[Advait251206]

From the snippet alone, it does look confusing, but the return isn't necessarily a bug—it depends on where it is in the control flow.

The intention of tools/preprocess_data.py is that when args.partitions == 1, the script should still preprocess the input and generate the .bin and .idx files. If the program is returning before the dataset builder/writer has been invoked, then that would indeed prevent any output from being produced.

A few things to check:

1. Which commit/version are you using?

   • The code has changed over time, so it's possible you're looking at an older revision where this was a bug that was later fixed.

2. Is the return inside a helper function?

   • Sometimes a return exits only a preprocessing stage (e.g., partitioning logic) rather than terminating the entire script. The surrounding context is important.

3. Are there any errors before the return?

   • If preprocessing fails earlier (e.g., tokenizer initialization or input parsing), the script may reach that branch without ever writing the indexed dataset.

If you're using commit 86e2927 and can confirm that running the exact command results in no .bin or .idx files being produced, despite no errors being reported, then this does sound like a legitimate issue worth investigating.

Could you also share:

• the exact commit or release you're using,
• whether the script exits successfully (exit code 0),
• and whether any intermediate files are created?

That would help determine whether this is expected behavior or a regression in that version.

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