Fix SequentialWorkflow to allow initialization without agents

docs/swarms/structs/sequential_workflow.md

@@ -41,13 +41,13 @@ graph TD
 
 ### `__init__(self, agents: List[Union[Agent, Callable]] = None, max_loops: int = 1, team_awareness: bool = False, *args, **kwargs)`
 
-The constructor initializes the `SequentialWorkflow` object.
+The constructor initializes the `SequentialWorkflow` object. Agents can be provided during initialization or the workflow can be initialized empty and configured later.
 
 - **Parameters:**
   - `id` (`str`, optional): Unique identifier for the workflow. Defaults to `"sequential_workflow"`.
   - `name` (`str`, optional): Name of the workflow. Defaults to `"SequentialWorkflow"`.
   - `description` (`str`, optional): Description of the workflow. Defaults to a standard description.
-  - `agents` (`List[Union[Agent, Callable]]`, optional): The list of agents or callables to execute in sequence.
+  - `agents` (`List[Union[Agent, Callable]]`, optional): The list of agents or callables to execute in sequence. Can be `None` during initialization but must be set before calling any run methods. Defaults to `None`.
   - `max_loops` (`int`, optional): The maximum number of loops to execute the workflow. Defaults to `1`.
   - `output_type` (`OutputType`, optional): Output format for the workflow. Defaults to `"dict"`.
   - `shared_memory_system` (`callable`, optional): Callable for shared memory management. Defaults to `None`.
@@ -56,6 +56,8 @@ The constructor initializes the `SequentialWorkflow` object.
   - `*args`: Variable length argument list.
   - `**kwargs`: Arbitrary keyword arguments.
 
+- **Note:** When initialized without agents, the workflow's `agent_rearrange` attribute will be `None` and `flow` will be an empty string. You must provide agents before running the workflow.
+
 ### `run(self, task: str, img: Optional[str] = None, imgs: Optional[List[str]] = None, *args, **kwargs) -> str`
 
 Runs the specified task through the agents in the dynamically constructed flow.
@@ -70,6 +72,9 @@ Runs the specified task through the agents in the dynamically constructed flow.
 - **Returns:**
   - The final result after processing through all agents.
 
+- **Raises:**
+  - `ValueError`: If agents list is None or empty when attempting to run.
+
 ### `run_batched(self, tasks: List[str]) -> List[str]`
 
 Executes a batch of tasks through the agents in the dynamically constructed flow.
@@ -80,6 +85,9 @@ Executes a batch of tasks through the agents in the dynamically constructed flow
 - **Returns:**
   - `List[str]`: A list of final results after processing through all agents.
 
+- **Raises:**
+  - `ValueError`: If agents list is None or empty when attempting to run.
+
 ### `async run_async(self, task: str) -> str`
 
 Executes the specified task through the agents asynchronously.
@@ -90,6 +98,9 @@ Executes the specified task through the agents asynchronously.
 - **Returns:**
   - `str`: The final result after processing through all agents.
 
+- **Raises:**
+  - `ValueError`: If agents list is None or empty when attempting to run.
+
 ### `async run_concurrent(self, tasks: List[str]) -> List[str]`
 
 Executes a batch of tasks through the agents concurrently.
@@ -100,6 +111,9 @@ Executes a batch of tasks through the agents concurrently.
 - **Returns:**
   - `List[str]`: A list of final results after processing through all agents.
 
+- **Raises:**
+  - `ValueError`: If agents list is None or empty when attempting to run.
+
 ## Usage Examples
 
 ### Basic Sequential Workflow
@@ -303,7 +317,7 @@ print(result)
 
 | Parameter | Description | Default |
 |-----------|-------------|---------|
-| `agents` | List of agents to execute in sequence | Required |
+| `agents` | List of agents to execute in sequence | None (optional at init, required before run) |
 | `name` | Name of the workflow | "SequentialWorkflow" |
 | `description` | Description of workflow purpose | Standard description |
 | `max_loops` | Number of times to execute workflow | 1 |
@@ -317,6 +331,29 @@ print(result)
 4. **System Prompts**: Write comprehensive system prompts that explain the agent's expertise and responsibilities.
 5. **Task Clarity**: Provide clear, specific tasks when calling `run()`.
 
+## Initialization Behavior
+
+The `SequentialWorkflow` can be initialized with or without agents:
+
+### With Agents (Standard)
+```python
+workflow = SequentialWorkflow(agents=[agent1, agent2, agent3])
+# Ready to run immediately
+workflow.run("Task to execute")
+```
+
+### Without Agents (Deferred Configuration)
+```python
+# Create an empty workflow
+workflow = SequentialWorkflow()
+
+# Configure later (you'll need to reinitialize with agents)
+workflow = SequentialWorkflow(agents=[agent1, agent2])
+workflow.run("Task to execute")
+```
+
+**Note**: When initialized without agents, `agent_rearrange` will be `None` and `flow` will be an empty string. You must provide agents before calling any execution methods.
+
 ## Logging and Error Handling
 
 The `run` method includes comprehensive logging to track workflow execution:
@@ -325,6 +362,19 @@ The `run` method includes comprehensive logging to track workflow execution:
 2023-05-08 10:30:15.456 | INFO | Sequential Workflow Name: SequentialWorkflow is ready to run.
 ```
 
+### Error Handling
+
+All execution methods (`run`, `run_batched`, `run_async`, `run_concurrent`) validate that agents are configured before execution:
+
+```python
+workflow = SequentialWorkflow()  # No agents
+
+try:
+    workflow.run("Some task")
+except ValueError as e:
+    print(e)  # "Agents list cannot be None or empty. Add agents before running the workflow."
+```
+
 All errors during execution are logged and re-raised for proper error handling.
 
 ## Accessing Workflow Information

swarms/structs/sequential_workflow.py

@@ -80,18 +80,23 @@ class SequentialWorkflow:
         self.multi_agent_collab_prompt = multi_agent_collab_prompt
         self.team_awareness = team_awareness
 
-        self.reliability_check()
-        self.flow = self.sequential_flow()
-
-        self.agent_rearrange = AgentRearrange(
-            name=self.name,
-            description=self.description,
-            agents=self.agents,
-            flow=self.flow,
-            max_loops=self.max_loops,
-            output_type=self.output_type,
-            team_awareness=self.team_awareness,
-        )
+        # Only validate and initialize if agents are provided
+        if self.agents is not None and len(self.agents) > 0:
+            self.reliability_check()
+            self.flow = self.sequential_flow()
+
+            self.agent_rearrange = AgentRearrange(
+                name=self.name,
+                description=self.description,
+                agents=self.agents,
+                flow=self.flow,
+                max_loops=self.max_loops,
+                output_type=self.output_type,
+                team_awareness=self.team_awareness,
+            )
+        else:
+            self.flow = ""
+            self.agent_rearrange = None
 
     def reliability_check(self):
         """
@@ -180,9 +185,15 @@ class SequentialWorkflow:
             str: The final result after processing through all agents.
 
         Raises:
-            ValueError: If the task is None or empty.
+            ValueError: If the task is None or empty, or if no agents are configured.
             Exception: If any error occurs during task execution.
         """
+        if self.agents is None or len(self.agents) == 0:
+            raise ValueError("Agents list cannot be None or empty. Add agents before running the workflow.")
+
+        if self.agent_rearrange is None:
+            raise ValueError("Workflow not properly initialized. AgentRearrange is None.")
+
         try:
             # prompt = f"{MULTI_AGENT_COLLAB_PROMPT}\n\n{task}"
             return self.agent_rearrange.run(
@@ -221,9 +232,15 @@ class SequentialWorkflow:
             List[str]: A list of final results after processing through all agents.
 
         Raises:
-            ValueError: If tasks is None, empty, or contains non-string elements.
+            ValueError: If tasks is None, empty, contains non-string elements, or if no agents are configured.
             Exception: If any error occurs during task execution.
         """
+        if self.agents is None or len(self.agents) == 0:
+            raise ValueError("Agents list cannot be None or empty. Add agents before running the workflow.")
+
+        if self.agent_rearrange is None:
+            raise ValueError("Workflow not properly initialized. AgentRearrange is None.")
+
         if not tasks or not all(
             isinstance(task, str) for task in tasks
         ):
@@ -250,9 +267,15 @@ class SequentialWorkflow:
             str: The final result after processing through all agents.
 
         Raises:
-            ValueError: If task is None or not a string.
+            ValueError: If task is None, not a string, or if no agents are configured.
             Exception: If any error occurs during task execution.
         """
+        if self.agents is None or len(self.agents) == 0:
+            raise ValueError("Agents list cannot be None or empty. Add agents before running the workflow.")
+
+        if self.agent_rearrange is None:
+            raise ValueError("Workflow not properly initialized. AgentRearrange is None.")
+
         if not task or not isinstance(task, str):
             raise ValueError("Task must be a non-empty string")
 
@@ -275,9 +298,15 @@ class SequentialWorkflow:
             List[str]: A list of final results after processing through all agents.
 
         Raises:
-            ValueError: If tasks is None, empty, or contains non-string elements.
+            ValueError: If tasks is None, empty, contains non-string elements, or if no agents are configured.
             Exception: If any error occurs during task execution.
         """
+        if self.agents is None or len(self.agents) == 0:
+            raise ValueError("Agents list cannot be None or empty. Add agents before running the workflow.")
+
+        if self.agent_rearrange is None:
+            raise ValueError("Workflow not properly initialized. AgentRearrange is None.")
+
         if not tasks or not all(
             isinstance(task, str) for task in tasks
         ):

tests/structs/test_sequential_workflow.py

@@ -7,15 +7,12 @@ from swarms import Agent, SequentialWorkflow
 def test_sequential_workflow_initialization():
     workflow = SequentialWorkflow()
     assert isinstance(workflow, SequentialWorkflow)
-    assert len(workflow.tasks) == 0
+    assert workflow.agents is None
     assert workflow.max_loops == 1
-    assert workflow.autosave is False
-    assert (
-        workflow.saved_state_filepath
-        == "sequential_workflow_state.json"
-    )
-    assert workflow.restore_state_filepath is None
-    assert workflow.dashboard is False
+    assert workflow.flow == ""
+    assert workflow.agent_rearrange is None
+    assert workflow.name == "SequentialWorkflow"
+    assert workflow.id == "sequential_workflow"
 
 
 def test_sequential_workflow_initialization_with_agents():
@@ -83,6 +80,11 @@ def test_sequential_workflow_multi_agent_execution():
     result = workflow.run(
         "Analyze the impact of renewable energy on climate change"
     )
+    print("\n" + "="*80)
+    print("WORKFLOW RESULT:")
+    print("="*80)
+    print(result)
+    print("="*80 + "\n")
     assert result is not None
     # SequentialWorkflow may return different types based on output_type, just ensure it's not None
 
@@ -232,16 +234,24 @@ def test_sequential_workflow_with_multi_agent_collaboration():
 
 def test_sequential_workflow_error_handling():
     """Test SequentialWorkflow error handling"""
-    # Test with invalid agents list
+    # Test that initialization with None agents is allowed
+    workflow_none = SequentialWorkflow(agents=None)
+    assert workflow_none.agents is None
+
+    # Test that initialization with empty agents is allowed
+    workflow_empty = SequentialWorkflow(agents=[])
+    assert workflow_empty.agents == []
+
+    # Test that running with no agents raises error
     with pytest.raises(
         ValueError, match="Agents list cannot be None or empty"
     ):
-        SequentialWorkflow(agents=None)
+        workflow_none.run("test task")
 
     with pytest.raises(
         ValueError, match="Agents list cannot be None or empty"
     ):
-        SequentialWorkflow(agents=[])
+        workflow_empty.run("test task")
 
     # Test with zero max_loops
     with pytest.raises(ValueError, match="max_loops cannot be 0"):