pocketflow/docs/utility_function/viz.md

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---
layout: default
title: "Viz and Debug"
parent: "Utility Function"
nav_order: 2
---
# Visualization and Debugging
Similar to LLM wrappers, we **don't** provide built-in visualization and debugging. Here, we recommend some *minimal* (and incomplete) implementations These examples can serve as a starting point for your own tooling.
## 1. Visualization with Mermaid
This code recursively traverses the nested graph, assigns unique IDs to each node, and treats Flow nodes as subgraphs to generate Mermaid syntax for a hierarchical visualization.
{% raw %}
```python
def build_mermaid(start):
ids, visited, lines = {}, set(), ["graph LR"]
ctr = 1
def get_id(n):
nonlocal ctr
return ids[n] if n in ids else (ids.setdefault(n, f"N{ctr}"), (ctr := ctr + 1))[0]
def link(a, b):
lines.append(f" {a} --> {b}")
def walk(node, parent=None):
if node in visited:
return parent and link(parent, get_id(node))
visited.add(node)
if isinstance(node, Flow):
node.start_node and parent and link(parent, get_id(node.start_node))
lines.append(f"\n subgraph sub_flow_{get_id(node)}[{type(node).__name__}]")
node.start_node and walk(node.start_node)
for nxt in node.successors.values():
node.start_node and walk(nxt, get_id(node.start_node)) or (parent and link(parent, get_id(nxt))) or walk(nxt)
lines.append(" end\n")
else:
lines.append(f" {(nid := get_id(node))}['{type(node).__name__}']")
parent and link(parent, nid)
[walk(nxt, nid) for nxt in node.successors.values()]
walk(start)
return "\n".join(lines)
```
{% endraw %}
For example, suppose we have a complex Flow for data science:
```python
class DataPrepBatchNode(BatchNode):
def prep(self,shared): return []
class ValidateDataNode(Node): pass
class FeatureExtractionNode(Node): pass
class TrainModelNode(Node): pass
class EvaluateModelNode(Node): pass
class ModelFlow(Flow): pass
class DataScienceFlow(Flow):pass
feature_node = FeatureExtractionNode()
train_node = TrainModelNode()
evaluate_node = EvaluateModelNode()
feature_node >> train_node >> evaluate_node
model_flow = ModelFlow(start=feature_node)
data_prep_node = DataPrepBatchNode()
validate_node = ValidateDataNode()
data_prep_node >> validate_node >> model_flow
data_science_flow = DataScienceFlow(start=data_prep_node)
result = build_mermaid(start=data_science_flow)
```
The code generates a Mermaid diagram:
```mermaid
graph LR
subgraph sub_flow_N1[DataScienceFlow]
N2['DataPrepBatchNode']
N3['ValidateDataNode']
N2 --> N3
N3 --> N4
subgraph sub_flow_N5[ModelFlow]
N4['FeatureExtractionNode']
N6['TrainModelNode']
N4 --> N6
N7['EvaluateModelNode']
N6 --> N7
end
end
```
For visualization based on d3.js, check out [the cookbook](https://github.com/The-Pocket/PocketFlow/tree/main/cookbook/pocketflow-visualization).
## 2. Call Stack Debugging
It would be useful to print the Node call stacks for debugging. This can be achieved by inspecting the runtime call stack:
```python
import inspect
def get_node_call_stack():
stack = inspect.stack()
node_names = []
seen_ids = set()
for frame_info in stack[1:]:
local_vars = frame_info.frame.f_locals
if 'self' in local_vars:
caller_self = local_vars['self']
if isinstance(caller_self, BaseNode) and id(caller_self) not in seen_ids:
seen_ids.add(id(caller_self))
node_names.append(type(caller_self).__name__)
return node_names
```
For example, suppose we have a complex Flow for data science:
```python
class DataPrepBatchNode(BatchNode):
def prep(self, shared): return []
class ValidateDataNode(Node): pass
class FeatureExtractionNode(Node): pass
class TrainModelNode(Node): pass
class EvaluateModelNode(Node):
def prep(self, shared):
stack = get_node_call_stack()
print("Call stack:", stack)
class ModelFlow(Flow): pass
class DataScienceFlow(Flow):pass
feature_node = FeatureExtractionNode()
train_node = TrainModelNode()
evaluate_node = EvaluateModelNode()
feature_node >> train_node >> evaluate_node
model_flow = ModelFlow(start=feature_node)
data_prep_node = DataPrepBatchNode()
validate_node = ValidateDataNode()
data_prep_node >> validate_node >> model_flow
data_science_flow = DataScienceFlow(start=data_prep_node)
data_science_flow.run({})
```
The output would be: `Call stack: ['EvaluateModelNode', 'ModelFlow', 'DataScienceFlow']`