ValueError
builtins.ValueError
Stack trace
Traceback (most recent call last):
File "app.py", line 42, in <module>
for chunk in instructor_client.stream_instructions(prompt):
File "instructor/streaming.py", line 88, in stream_instructions
raise ValueError('Partial streaming output detected, incomplete data chunk')
ValueError: Partial streaming output detected, incomplete data chunk Why it happens
This error happens because the Instructor client expects a fully formed data chunk in each streamed iteration. If the streaming connection is interrupted or the model returns incomplete data, the iterable cannot yield a valid chunk, triggering this error.
Detection
Monitor streaming output for incomplete or truncated chunks and catch ValueError exceptions during iteration to log partial data before failure.
Causes & fixes
Network interruption or timeout during streaming causing incomplete data chunks
Implement retry logic on streaming calls and increase network timeout settings to ensure full data chunks are received.
Model or API returning partial or malformed streaming responses
Switch to a stable, instruction-tuned model version and verify the prompt format to ensure consistent streaming output.
Incorrect handling of the streaming iterable, consuming before full chunk is ready
Use the provided async or sync iterator methods as documented, avoiding premature consumption of the stream.
Code: broken vs fixed
from instructor import InstructorClient
client = InstructorClient(api_key="mykey")
prompt = "Explain AI in simple terms"
# This line triggers the partial streaming error
for chunk in client.stream_instructions(prompt):
print(chunk)import os
from instructor import InstructorClient
client = InstructorClient(api_key=os.environ["INSTRUCTOR_API_KEY"])
prompt = "Explain AI in simple terms"
try:
for chunk in client.stream_instructions(prompt):
print(chunk)
except ValueError as e:
print(f"Partial streaming error caught: {e}")
# Optionally retry or handle fallback hereWorkaround
Catch the ValueError during streaming iteration, buffer partial chunks manually, and attempt to reconstruct or request the missing data before retrying.
Prevention
Use robust streaming client implementations with built-in retry and chunk validation, and prefer stable instruction-tuned models that produce consistent streaming outputs.