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Merge pull request #4009 from pipecat-ai/pk/perplexity-message-ordering-strictness

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Add PerplexityLLMAdapter for message ordering strictness
This commit is contained in:
kompfner
2026-03-12 16:51:11 -04:00
committed by GitHub
parent 43a2d55c61 99f28120b7
commit 30d95e3b84
9 changed files with 398 additions and 4 deletions
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152
src/pipecat/adapters/services/perplexity_adapter.py Normal file
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@@ -0,0 +1,152 @@
#
# Copyright (c) 2024-2026, Daily
#
# SPDX-License-Identifier: BSD 2-Clause License
#
"""Perplexity LLM adapter for Pipecat.
Perplexity's API uses an OpenAI-compatible interface but enforces stricter
constraints on conversation history structure:
1. **Strict role alternation** — Messages must alternate between "user"/"tool"
and "assistant" roles. Consecutive messages with the same role (e.g. two
"user" messages in a row) are rejected with:
``"messages must be an alternating sequence of user/tool and assistant messages"``
2. **No non-initial system messages** — "system" messages are only allowed at
the start of the conversation. A system message after a non-system message
causes:
``"only the initial message can have the system role"``
3. **Last message must be user/tool** — The final message in the conversation
must have role "user" or "tool". A trailing "assistant" message causes:
``"the last message must have the user or tool role"``
This adapter transforms the message list to satisfy all three constraints before
the messages are sent to Perplexity's API.
"""
import copy
from typing import List
from openai.types.chat import ChatCompletionMessageParam
from pipecat.adapters.services.open_ai_adapter import OpenAILLMAdapter, OpenAILLMInvocationParams
from pipecat.processors.aggregators.llm_context import LLMContext
class PerplexityLLMAdapter(OpenAILLMAdapter):
"""Adapter that transforms messages to satisfy Perplexity's API constraints.
Perplexity's API is stricter than OpenAI about message structure. This
adapter extends ``OpenAILLMAdapter`` and applies message transformations
to ensure compliance with Perplexity's constraints (role alternation,
no non-initial system messages, last message must be user/tool).
The transformations are applied in ``get_llm_invocation_params`` after the
parent adapter extracts messages from the LLM context, and before
``build_chat_completion_params`` prepends ``system_instruction``.
"""
def get_llm_invocation_params(self, context: LLMContext) -> OpenAILLMInvocationParams:
"""Get OpenAI-compatible invocation parameters with Perplexity message fixes applied.
Args:
context: The LLM context containing messages, tools, etc.
Returns:
Dictionary of parameters for Perplexity's ChatCompletion API, with
messages transformed to satisfy Perplexity's constraints.
"""
params = super().get_llm_invocation_params(context)
params["messages"] = self._transform_messages(list(params["messages"]))
return params
def _transform_messages(
self, messages: List[ChatCompletionMessageParam]
) -> List[ChatCompletionMessageParam]:
"""Transform messages to satisfy Perplexity's API constraints.
Applies three transformation steps in order:
1. **Convert non-initial system messages to user** — Any system message
after the initial system message block is converted to role "user",
since Perplexity rejects system messages after a non-system message.
2. **Merge consecutive same-role messages** — After the above
conversions, adjacent messages with the same role are merged using
list-of-dicts content format. This ensures strict role alternation
(e.g. a converted system→user message adjacent to an existing user
message gets merged).
3. **Remove trailing assistant messages** — If the last message is
"assistant", remove it. OpenAI appears to silently ignore trailing
assistant messages server-side, so removing them preserves equivalent
behavior while satisfying Perplexity's "last message must be
user/tool" constraint.
Note: we intentionally do *not* convert a trailing system message to
"user". That would make the transformation unstable across calls —
Perplexity appears to have statefulness/caching within a conversation,
so a message that was sent as "user" in one call but becomes "system"
in the next (once more messages are appended) causes errors. If the
context consists entirely of system messages, the Perplexity API call
will fail, but that mistake will be caught right away.
Args:
messages: List of message dicts with "role" and "content" keys.
Returns:
Transformed list of message dicts satisfying Perplexity's constraints.
"""
if not messages:
return messages
messages = copy.deepcopy(messages)
# Step 1: Convert non-initial system messages to "user".
# Perplexity allows system messages at the start, but rejects them
# after any non-system message.
in_initial_system_block = True
for i in range(len(messages)):
if messages[i].get("role") == "system":
if not in_initial_system_block:
messages[i]["role"] = "user"
else:
in_initial_system_block = False
# Step 2: Merge consecutive same-role messages.
# After system→user conversions above, we may have adjacent same-role
# messages that violate Perplexity's strict alternation requirement.
# Skip consecutive system messages at the start — Perplexity allows those.
i = 0
while i < len(messages) - 1:
current = messages[i]
next_msg = messages[i + 1]
if current["role"] == next_msg["role"] == "system":
# Perplexity allows multiple initial system messages, don't merge
i += 1
elif current["role"] == next_msg["role"]:
# Convert string content to list-of-dicts format for merging
if isinstance(current.get("content"), str):
current["content"] = [{"type": "text", "text": current["content"]}]
if isinstance(next_msg.get("content"), str):
next_msg["content"] = [{"type": "text", "text": next_msg["content"]}]
# Merge content from next message into current
if isinstance(current.get("content"), list) and isinstance(
next_msg.get("content"), list
):
current["content"].extend(next_msg["content"])
messages.pop(i + 1)
else:
i += 1
# Step 3: Remove trailing assistant messages.
# Perplexity requires the last message to be "user" or "tool".
# OpenAI appears to silently ignore trailing assistant messages
# server-side, so removing them preserves equivalent behavior.
while messages and messages[-1].get("role") == "assistant":
messages.pop()
return messages

4
src/pipecat/services/cerebras/llm.py
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@@ -117,6 +117,10 @@ class CerebrasLLMService(OpenAILLMService):
# Prepend system instruction if set
if self._settings.system_instruction:
messages = params.get("messages", [])
if messages and messages[0].get("role") == "system":
logger.warning(
f"{self}: Both system_instruction and an initial system message in context are set. This may be unintended."
)
params["messages"] = [
{"role": "system", "content": self._settings.system_instruction}
] + messages

4
src/pipecat/services/fireworks/llm.py
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@@ -118,6 +118,10 @@ class FireworksLLMService(OpenAILLMService):
# Prepend system instruction if set
if self._settings.system_instruction:
messages = params.get("messages", [])
if messages and messages[0].get("role") == "system":
logger.warning(
f"{self}: Both system_instruction and an initial system message in context are set. This may be unintended."
)
params["messages"] = [
{"role": "system", "content": self._settings.system_instruction}
] + messages

4
src/pipecat/services/mistral/llm.py
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@@ -236,6 +236,10 @@ class MistralLLMService(OpenAILLMService):
# Prepend system instruction if set
if self._settings.system_instruction:
messages = params.get("messages", [])
if messages and messages[0].get("role") == "system":
logger.warning(
f"{self}: Both system_instruction and an initial system message in context are set. This may be unintended."
)
params["messages"] = [
{"role": "system", "content": self._settings.system_instruction}
] + messages

6
src/pipecat/services/openai/base_llm.py
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@@ -332,8 +332,7 @@ class BaseOpenAILLMService(LLMService):
messages = params.get("messages", [])
if messages and messages[0].get("role") == "system":
logger.warning(
f"{self}: Both system_instruction and a system message in context are set."
" Using system_instruction."
f"{self}: Both system_instruction and an initial system message in context are set. This may be unintended."
)
params["messages"] = [
{"role": "system", "content": self._settings.system_instruction}
@@ -381,8 +380,7 @@ class BaseOpenAILLMService(LLMService):
messages = params.get("messages", [])
if messages and messages[0].get("role") == "system":
logger.warning(
f"{self}: Both system_instruction and a system message in context are set."
" Using system_instruction."
f"{self}: Both system_instruction and an initial system message in context are set. This may be unintended."
)
params["messages"] = [{"role": "system", "content": system_instruction}] + messages

9
src/pipecat/services/perplexity/llm.py
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@@ -14,7 +14,10 @@ reporting patterns while maintaining compatibility with the Pipecat framework.
from dataclasses import dataclass
from typing import Optional
from loguru import logger
from pipecat.adapters.services.open_ai_adapter import OpenAILLMInvocationParams
from pipecat.adapters.services.perplexity_adapter import PerplexityLLMAdapter
from pipecat.metrics.metrics import LLMTokenUsage
from pipecat.processors.aggregators.llm_context import LLMContext
from pipecat.processors.aggregators.openai_llm_context import OpenAILLMContext
@@ -37,6 +40,8 @@ class PerplexityLLMService(OpenAILLMService):
in token usage reporting between Perplexity (incremental) and OpenAI (final summary).
"""
adapter_class = PerplexityLLMAdapter
Settings = PerplexityLLMSettings
_settings: Settings
@@ -119,6 +124,10 @@ class PerplexityLLMService(OpenAILLMService):
# Prepend system instruction if set
if self._settings.system_instruction:
messages = params.get("messages", [])
if messages and messages[0].get("role") == "system":
logger.warning(
f"{self}: Both system_instruction and an initial system message in context are set. This may be unintended."
)
params["messages"] = [
{"role": "system", "content": self._settings.system_instruction}
] + messages

4
src/pipecat/services/sambanova/llm.py
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@@ -134,6 +134,10 @@ class SambaNovaLLMService(OpenAILLMService): # type: ignore
# Prepend system instruction if set
if self._settings.system_instruction:
messages = params.get("messages", [])
if messages and messages[0].get("role") == "system":
logger.warning(
f"{self}: Both system_instruction and an initial system message in context are set. This may be unintended."
)
params["messages"] = [
{"role": "system", "content": self._settings.system_instruction}
] + messages