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fix(prompt): preserve empty fallback values #1828

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fix(prompt): preserve empty fallback values #1828

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2 changes: 1 addition & 1 deletion langfuse/_client/client.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3919,7 +3919,7 @@ def get_prompt(
fetch_timeout_seconds=fetch_timeout_seconds,
)
except Exception as e:
if fallback:
if fallback is not None:
langfuse_logger.warning(
f"Returning fallback prompt for '{cache_key}' due to fetch error: {e}"
)
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13 changes: 13 additions & 0 deletions tests/unit/test_prompt.py
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Original file line number Diff line number Diff line change
Expand Up @@ -222,6 +222,19 @@ def test_throw_when_failing_fetch_and_no_cache(langfuse):
assert "Prompt not found" in str(exc_info.value)


def test_returns_empty_text_fallback_when_fetch_fails(langfuse):
prompt_name = "test_returns_empty_text_fallback_when_fetch_fails"

mock_server_call = langfuse.api.prompts.get
mock_server_call.side_effect = Exception("Prompt not found")

result = langfuse.get_prompt(prompt_name, fallback="", max_retries=0)

assert result.is_fallback
assert result.prompt == ""
mock_server_call.assert_called_once()


def test_using_custom_prompt_timeouts(langfuse):
prompt_name = "test_using_custom_prompt_timeouts"
prompt = Prompt_Text(
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