Plexe provides a callback system that allows you to hook into various stages of the model.build() process. This is useful for logging, monitoring, custom artifact handling, or triggering external processes.

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The Callback System

Callbacks are classes that inherit from plexe.Callback and implement one or more of the following methods:
  • on_build_start(info: BuildStateInfo): Called once at the beginning of the build process.
  • on_build_end(info: BuildStateInfo): Called once at the end of the build process (after success or error).
  • on_iteration_start(info: BuildStateInfo): Called at the start of each model building iteration (solution attempt).
  • on_iteration_end(info: BuildStateInfo): Called at the end of each model building iteration.
The BuildStateInfo object passed to these methods contains contextual information like the model intent, provider used, schemas, datasets, current iteration number, and the current solution Node being evaluated (especially relevant in on_iteration_end).

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Built-in Callbacks

Plexe includes some useful built-in callbacks:

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MLFlowCallback

This callback logs parameters, metrics, and artifacts from the build process to an MLflow Tracking server. Prerequisites:
  1. Install MLflow: pip install mlflow
  2. Have an MLflow tracking server running or use local file logging.
Usage: 
import plexe
import pandas as pd
from plexe.callbacks import MLFlowCallback # Import the callback

# --- Prepare Data (as in Quickstart) ---
try:
    df = pd.read_csv("housing_data.csv")
except FileNotFoundError:
    df = pd.DataFrame({ # Dummy data
        'square_footage': [1500, 2100, 1800, 2500, 1200], 'bedrooms': [3, 4, 3, 5, 2],
        'bathrooms': [2, 2.5, 2, 3, 1.5], 'price': [300000, 450000, 380000, 550000, 250000]
    })
datasets = [df]
# -----------------------------------------

# --- Define Model (as in Quickstart) ---
model = plexe.Model(
    intent="Predict house prices based on square footage, bedrooms, and bathrooms."
)
# -----------------------------------------

# Configure MLflow tracking URI (local example)
# Replace with your tracking server URI if applicable (e.g., "http://localhost:5000")
mlflow_tracking_uri = "file:./mlruns"
mlflow_experiment_name = "Plexe_House_Pricing"

# Instantiate the callback
mlflow_callback = MLFlowCallback(
    tracking_uri=mlflow_tracking_uri,
    experiment_name=mlflow_experiment_name
)

print(f"Configured MLflow logging to: {mlflow_tracking_uri}, Experiment: {mlflow_experiment_name}")

# Build the model, passing the callback instance
print("Starting model build with MLflow logging...")
model.build(
    datasets=datasets,
    provider="openai/gpt-4o-mini",
    max_iterations=3, # Keep low for quick example
    callbacks=[mlflow_callback], # Pass the callback here
    chain_of_thought=False # Optional: disable default console logging if desired
)

print(f"Model build finished. Check MLflow UI for experiment '{mlflow_experiment_name}'.")
print(f"You can start the local MLflow UI with: mlflow ui --backend-store-uri {mlflow_tracking_uri}")

# You can now inspect the runs in the MLflow UI. Each iteration
# will be logged as a separate run within the specified experiment.
The MLFlowCallback logs:
  • Parameters: Intent, provider, schemas, timeouts, iteration number.
  • Metrics: Performance metrics (e.g., accuracy, RMSE) reported by the agent for each iteration, execution time.
  • Artifacts: Training code (trainer_source.py), model artifacts saved by the training script.
  • Tags: Provider used, whether an exception occurred during the iteration.

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Creating Custom Callbacks

You can create your own callbacks by subclassing plexe.Callback. Example: A simple callback to print iteration progress. 
import plexe
import pandas as pd
from plexe.callbacks import Callback, BuildStateInfo # Import base class and info object

# --- Prepare Data & Model (as before) ---
try:
    df = pd.read_csv("housing_data.csv")
except FileNotFoundError:
    df = pd.DataFrame({ # Dummy data
        'square_footage': [1500, 2100, 1800, 2500, 1200], 'bedrooms': [3, 4, 3, 5, 2],
        'bathrooms': [2, 2.5, 2, 3, 1.5], 'price': [300000, 450000, 380000, 550000, 250000]
    })
datasets = [df]
model = plexe.Model(intent="Predict house prices based on square footage, bedrooms, and bathrooms.")
# ---------------------------------------

# Define a custom callback
class ProgressPrinterCallback(Callback):
    def on_build_start(self, info: BuildStateInfo) -> None:
        print(f"🚀 Starting build for intent: '{info.intent[:50]}...'")
        if info.max_iterations:
             print(f"Max iterations: {info.max_iterations}")

    def on_iteration_start(self, info: BuildStateInfo) -> None:
        print(f"\n--- Iteration {info.iteration + 1} Start ---")

    def on_iteration_end(self, info: BuildStateInfo) -> None:
        print(f"--- Iteration {info.iteration + 1} End ---")
        if info.node: # Check if node info is available
             if info.node.performance:
                 print(f"  Performance ({info.node.performance.name}): {info.node.performance.value:.4f}")
             else:
                 print("  Performance: Not available")

             if info.node.exception_was_raised:
                 print(f"  Status: Failed ({type(info.node.exception).__name__})")
             else:
                 print("  Status: Success")
        else:
             print("  Node info not available for this iteration.")


    def on_build_end(self, info: BuildStateInfo) -> None:
        print(f"\n✅ Build process finished.")

# Instantiate the custom callback
progress_callback = ProgressPrinterCallback()

# Build the model with the custom callback
model.build(
    datasets=datasets,
    provider="openai/gpt-4o-mini",
    max_iterations=2,
    callbacks=[progress_callback], # Add custom callback
    chain_of_thought=False # Disable default verbose logging
)
By implementing custom callbacks, you can integrate Plexe’s model building process seamlessly into your existing workflows and monitoring systems.