langchain.smith.evaluation.progress.ProgressBarCallback: Make output after progress bar ends configurable

[dennism-tulcolabs]

Description

As currently written, any print/logging statements that occur after the progress bar has reached 100% end up sandwiched against the progress bar output, because ProgressBarCallback._print_bar() always sets end="" in its print statement. To address the issue, This PR implements a small change in ProgressBarCallback._print_bar(), where it invokes print(..., end="") when self.counter < self.total, and print(..., end=self.end_with) otherwise, where end_with is a new __init__ param (default = "\n").

Outcomes

Current Behavior

Under the current behavior, running the following:

start = time.time()

progress_bar = ProgressBarCallback(total=10, ncols=50)
runnable.batch_as_completed(
    inputs=...,
    config=RunnableConfig(callbacks=[progress_bar])
)

end = time.time()
print(f"Total processing time: {round(end - start)} secs")

Produces something that looks like:

[------------------------------------------------->] 10/10Total processing time: 35 secs  # 'Total ...' would ideally be on new line

New Behavior

With the change in this PR, the output from the previous example would look like the following:

[------------------------------------------------->] 10/10
Total processing time: 35 secs

Now, suppose the user wants to print "DONE." once the progress bar is complete, and have the "Total time ..." message to appear on the next line. They can now accomplish this via `progress_bar = ProgressBarCallback(total=10, ncols=50, end_with=" Done.\n"), which produces:

[------------------------------------------------->] 10/10 DONE.
Total processing time: 35 secs

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1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
langchain	⬜️ Ignored (Inspect)	Visit Preview		Jun 12, 2025 3:53pm

[codspeed-hq]

CodSpeed Walltime Performance Report

Merging #31583 will not alter performance

_{Comparing dennism-tulcolabs:progressbar-newline-at-end (42824b9) with master (446a9d5)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched benchmarks

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #31583 will not alter performance

_{Comparing dennism-tulcolabs:progressbar-newline-at-end (42824b9) with master (446a9d5)}

Summary

✅ 13 untouched benchmarks

[dennism-tulcolabs]

@baskaryan - just checking in on whether you or anyone else on your team has had a chance to review this?