problems with generated exponential histogram

Describe your environment

Running with:

• MacBook Pro Intel
• MacOS 14.3.1 (intel)
• Python 3.11.7 (homebrew)

Requirements:

opentelemetry-api>=1.23.0
opentelemetry-sdk>=1.23.0
opentelemetry-proto>=1.23.0
opentelemetry-exporter-otlp>=1.23.0

Steps to reproduce

Run main.py (below) and capture the dump of the exponential histogram.
Source code:

from opentelemetry import metrics
from opentelemetry.exporter.otlp.proto.http.metric_exporter import OTLPMetricExporter
from opentelemetry.sdk.metrics import MeterProvider
from opentelemetry.sdk.metrics.export import PeriodicExportingMetricReader

def main():

    exporter = OTLPMetricExporter()
    meter_provider = MeterProvider([PeriodicExportingMetricReader(exporter)])
    meter = metrics.get_meter(
        name="test-histogram",
        meter_provider=meter_provider,
    )
    histo = meter.create_histogram("test-histogram")
    for i in range(1000):
        for _ in range(i):
            histo.record(i, {"type": "test-histogram"})

    meter_provider.shutdown()

if __name__ == "__main__":
    main()

This is run with the following script:

export OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318
export OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE=DELTA
export OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION=base2_exponential_bucket_histogram

python3 ./main.py

What is the expected behavior?

I expected to see a dump like that generated for the JavaScript SDK in
dump-js.txt.

What is the actual behavior?

The generated exponential histogram in dump-python.txt seems to have the following problems:

1. There is a negative bucket, even though no negative values are added to the histogram. (This actually causes a downstream vendor to reject the histogram.)
2. All 160 buckets are provided even though the last 79 are all empty. Other SDKs (e.g. Javascript, dump-js.txt) trim unnecessary buckets, reducing the size of the payload.

Additional context

None.

Start by running the provided main.py with the listed OTLP and exponential-histogram environment variables, then compare dump-python.txt with dump-js.txt. Trace the Python SDK's exponential histogram generation to determine why a negative bucket appears and why trailing empty buckets are retained. Done means the output has no negative bucket for these nonnegative values and omits unnecessary trailing empty buckets.