refactor: Replace check of instance for LlmAgent with hasAttribute check

Co-authored-by: Xiang (Sean) Zhou <seanzhougoogle@google.com>
PiperOrigin-RevId: 868370272

src/google/adk/auth/auth_preprocessor.py

@@ -15,7 +15,6 @@
 from __future__ import annotations
 
 from typing import AsyncGenerator
-from typing import TYPE_CHECKING
 
 from typing_extensions import override
 
@@ -30,9 +29,6 @@ from .auth_handler import AuthHandler
 from .auth_tool import AuthConfig
 from .auth_tool import AuthToolArguments
 
-if TYPE_CHECKING:
-  from ..agents.llm_agent import LlmAgent
-
 # Prefix used by toolset auth credential IDs.
 # Auth requests with this prefix are for toolset authentication (before tool
 # listing) and don't require resuming a function call.
@@ -46,10 +42,8 @@ class _AuthLlmRequestProcessor(BaseLlmRequestProcessor):
   async def run_async(
       self, invocation_context: InvocationContext, llm_request: LlmRequest
   ) -> AsyncGenerator[Event, None]:
-    from ..agents.llm_agent import LlmAgent
-
     agent = invocation_context.agent
-    if not isinstance(agent, LlmAgent):
+    if not hasattr(agent, 'canonical_tools'):
       return
     events = invocation_context.session.events
     if not events:

src/google/adk/flows/llm_flows/_code_execution.py

@@ -120,9 +120,7 @@ class _CodeExecutionRequestProcessor(BaseLlmRequestProcessor):
   async def run_async(
       self, invocation_context: InvocationContext, llm_request: LlmRequest
   ) -> AsyncGenerator[Event, None]:
-    from ...agents.llm_agent import LlmAgent
-
-    if not isinstance(invocation_context.agent, LlmAgent):
+    if not hasattr(invocation_context.agent, 'code_executor'):
       return
     if not invocation_context.agent.code_executor:
       return
@@ -175,9 +173,7 @@ async def _run_pre_processor(
     llm_request: LlmRequest,
 ) -> AsyncGenerator[Event, None]:
   """Pre-process the user message by adding the user message to the Colab notebook."""
-  from ...agents.llm_agent import LlmAgent
-
-  if not isinstance(invocation_context.agent, LlmAgent):
+  if not hasattr(invocation_context.agent, 'code_executor'):
     return
 
   agent = invocation_context.agent

src/google/adk/flows/llm_flows/_nl_planning.py

@@ -109,11 +109,10 @@ response_processor = _NlPlanningResponse()
 def _get_planner(
     invocation_context: InvocationContext,
 ) -> Optional[BasePlanner]:
-  from ...agents.llm_agent import Agent
   from ...planners.base_planner import BasePlanner
 
   agent = invocation_context.agent
-  if not isinstance(agent, Agent):
+  if not hasattr(agent, 'planner'):
     return None
   if not agent.planner:
     return None

src/google/adk/flows/llm_flows/agent_transfer.py

@@ -40,9 +40,7 @@ class _AgentTransferLlmRequestProcessor(BaseLlmRequestProcessor):
   async def run_async(
       self, invocation_context: InvocationContext, llm_request: LlmRequest
   ) -> AsyncGenerator[Event, None]:
-    from ...agents.llm_agent import LlmAgent
-
-    if not isinstance(invocation_context.agent, LlmAgent):
+    if not hasattr(invocation_context.agent, 'disallow_transfer_to_parent'):
       return
 
     transfer_targets = _get_transfer_targets(invocation_context.agent)
@@ -141,12 +139,12 @@ If neither you nor the other agents are best for the question, transfer to your
 
 
 def _get_transfer_targets(agent: LlmAgent) -> list[BaseAgent]:
-  from ...agents.llm_agent import LlmAgent
-
   result = []
   result.extend(agent.sub_agents)
 
-  if not agent.parent_agent or not isinstance(agent.parent_agent, LlmAgent):
+  if not agent.parent_agent or not hasattr(
+      agent.parent_agent, 'disallow_transfer_to_parent'
+  ):
     return result
 
   if not agent.disallow_transfer_to_parent:

src/google/adk/flows/llm_flows/base_llm_flow.py

@@ -520,12 +520,11 @@ class BaseLlmFlow(ABC):
   async def _preprocess_async(
       self, invocation_context: InvocationContext, llm_request: LlmRequest
   ) -> AsyncGenerator[Event, None]:
-    from ...agents.llm_agent import LlmAgent
-
     agent = invocation_context.agent
-    if not isinstance(agent, LlmAgent):
+    if not hasattr(agent, 'tools') or not hasattr(agent, 'canonical_model'):
       raise TypeError(
-          f'Expected agent to be an LlmAgent, but got {type(agent)}'
+          'Expected agent to have tools and canonical_model attributes,'
+          f' but got {type(agent)}'
       )
 
     # Runs processors.
@@ -973,8 +972,6 @@ class BaseLlmFlow(ABC):
       llm_request: LlmRequest,
       model_response_event: Event,
   ) -> Optional[LlmResponse]:
-    from ...agents.llm_agent import LlmAgent
-
     agent = invocation_context.agent
 
     callback_context = CallbackContext(
@@ -1010,8 +1007,6 @@ class BaseLlmFlow(ABC):
       llm_response: LlmResponse,
       model_response_event: Event,
   ) -> Optional[LlmResponse]:
-    from ...agents.llm_agent import LlmAgent
-
     agent = invocation_context.agent
 
     # Add grounding metadata to the response if needed.
@@ -1130,12 +1125,11 @@ class BaseLlmFlow(ABC):
       A generator of LlmResponse.
     """
 
-    from ...agents.llm_agent import LlmAgent
-
     agent = invocation_context.agent
-    if not isinstance(agent, LlmAgent):
+    if not hasattr(agent, 'canonical_on_model_error_callbacks'):
       raise TypeError(
-          f'Expected agent to be an LlmAgent, but got {type(agent)}'
+          'Expected agent to have canonical_on_model_error_callbacks'
+          f' attribute, but got {type(agent)}'
       )
 
     async def _run_on_model_error_callbacks(
@@ -1190,6 +1184,10 @@ class BaseLlmFlow(ABC):
         raise model_error
 
   def __get_llm(self, invocation_context: InvocationContext) -> BaseLlm:
-    from ...agents.llm_agent import LlmAgent
-
-    return cast(LlmAgent, invocation_context.agent).canonical_model
+    agent = invocation_context.agent
+    if not hasattr(agent, 'canonical_model'):
+      raise TypeError(
+          'Expected agent to have canonical_model attribute,'
+          f' but got {type(agent)}'
+      )
+    return agent.canonical_model

src/google/adk/flows/llm_flows/instructions.py

@@ -73,7 +73,6 @@ async def _build_instructions(
     llm_request: The LlmRequest to populate with instructions.
   """
   from ...agents.base_agent import BaseAgent
-  from ...agents.llm_agent import LlmAgent
 
   agent = invocation_context.agent
 
@@ -81,7 +80,10 @@ async def _build_instructions(
 
   # Handle global instructions (DEPRECATED - use GlobalInstructionPlugin instead)
   # TODO: Remove this code block when global_instruction field is removed
-  if isinstance(root_agent, LlmAgent) and root_agent.global_instruction:
+  if (
+      hasattr(root_agent, 'global_instruction')
+      and root_agent.global_instruction
+  ):
     raw_si, bypass_state_injection = (
         await root_agent.canonical_global_instruction(
             ReadonlyContext(invocation_context)

src/google/adk/flows/llm_flows/interactions_processor.py

@@ -46,12 +46,11 @@ class InteractionsRequestProcessor(BaseLlmRequestProcessor):
     Yields:
         Event: No events are yielded by this processor
     """
-    from ...agents.llm_agent import LlmAgent
     from ...models.google_llm import Gemini
 
     agent = invocation_context.agent
     # Only process if using Gemini with interactions API
-    if not isinstance(agent, LlmAgent):
+    if not hasattr(agent, 'canonical_model'):
       return
     model = agent.canonical_model
     if not isinstance(model, Gemini):

src/google/adk/runners.py

@@ -39,7 +39,6 @@ from .agents.context_cache_config import ContextCacheConfig
 from .agents.invocation_context import InvocationContext
 from .agents.invocation_context import new_invocation_context_id
 from .agents.live_request_queue import LiveRequestQueue
-from .agents.llm_agent import LlmAgent
 from .agents.run_config import RunConfig
 from .apps.app import App
 from .apps.app import ResumabilityConfig
@@ -1143,8 +1142,8 @@ class Runner:
     """
     agent = agent_to_run
     while agent:
-      if not isinstance(agent, LlmAgent):
-        # Only LLM-based Agent can provide agent transfer capability.
+      if not hasattr(agent, 'disallow_transfer_to_parent'):
+        # Only agents with transfer capability can transfer.
         return False
       if agent.disallow_transfer_to_parent:
         return False
@@ -1393,7 +1392,7 @@ class Runner:
     run_config = run_config or RunConfig()
     invocation_id = invocation_id or new_invocation_context_id()
 
-    if run_config.support_cfc and isinstance(self.agent, LlmAgent):
+    if run_config.support_cfc and hasattr(self.agent, 'canonical_model'):
       model_name = self.agent.canonical_model.model
       if not model_name.startswith('gemini-2'):
         raise ValueError(
@@ -1487,7 +1486,7 @@ class Runner:
 
   def _collect_toolset(self, agent: BaseAgent) -> set[BaseToolset]:
     toolsets = set()
-    if isinstance(agent, LlmAgent):
+    if hasattr(agent, 'tools'):
       for tool_union in agent.tools:
         if isinstance(tool_union, BaseToolset):
           toolsets.add(tool_union)