Experiment tracking (MLflow) in ML Python

Introduction

Experiment tracking helps you keep a clear record of your machine learning tests. MLflow makes it easy to save and compare your model results.

You want to remember which model settings gave the best results.

You need to compare different model versions to pick the best one.

You want to share your experiment results with teammates.

You want to keep track of metrics like accuracy or loss during training.

You want to save models and their details for future use.

Syntax

ML Python

import mlflow

with mlflow.start_run():
    mlflow.log_param("param_name", param_value)
    mlflow.log_metric("metric_name", metric_value)
    mlflow.log_artifact("path_to_file")
    mlflow.sklearn.log_model(model, "model")

Use mlflow.start_run() to begin tracking an experiment.

Log parameters, metrics, artifacts, and models inside the run block.

Examples

This logs a learning rate parameter and accuracy metric for one run.

ML Python

import mlflow

with mlflow.start_run():
    mlflow.log_param("learning_rate", 0.01)
    mlflow.log_metric("accuracy", 0.85)

This logs a parameter, a metric, and saves a model file as an artifact.

ML Python

import mlflow

with mlflow.start_run():
    mlflow.log_param("max_depth", 5)
    mlflow.log_metric("rmse", 3.2)
    mlflow.log_artifact("model.pkl")

Sample Model

This program trains a simple Random Forest on iris data, logs parameters, accuracy, and the model using MLflow.

ML Python

import mlflow
import mlflow.sklearn
from sklearn.datasets import load_iris
from sklearn.model_selection import train_test_split
from sklearn.ensemble import RandomForestClassifier
from sklearn.metrics import accuracy_score

# Load data
iris = load_iris()
X_train, X_test, y_train, y_test = train_test_split(iris.data, iris.target, test_size=0.3, random_state=42)

# Start MLflow experiment
with mlflow.start_run():
    # Set and log parameter
    n_estimators = 10
    mlflow.log_param("n_estimators", n_estimators)

    # Train model
    model = RandomForestClassifier(n_estimators=n_estimators, random_state=42)
    model.fit(X_train, y_train)

    # Predict and calculate accuracy
    preds = model.predict(X_test)
    acc = accuracy_score(y_test, preds)

    # Log metric
    mlflow.log_metric("accuracy", acc)

    # Log model
    mlflow.sklearn.log_model(model, "random_forest_model")

    print(f"Logged run with accuracy: {acc:.4f}")

Important Notes

MLflow saves experiments locally by default in an 'mlruns' folder.

You can view logged experiments using the MLflow UI by running mlflow ui in your terminal.

Always start a run with mlflow.start_run() to group logs together.

Summary

MLflow helps you track your machine learning experiments easily.

You can log parameters, metrics, artifacts, and models to compare results later.

Use the MLflow UI to visualize and manage your experiments.

Practice

1. What is the main purpose of using MLflow in machine learning projects?

easy

A. To write machine learning algorithms from scratch

B. To visualize data without any coding

C. To track and manage machine learning experiments

D. To deploy machine learning models to mobile apps

Solution

1. Step 1: Understand MLflow's role

   MLflow is designed to help track experiments by logging parameters, metrics, and models.

2. Step 2: Compare options

   Options A, C, and D describe tasks outside MLflow's main purpose.

3. Final Answer:

   To track and manage machine learning experiments -> Option C

4. Quick Check:

   MLflow = experiment tracking [OK]

Hint: MLflow is for tracking experiments, not coding models [OK]

Common Mistakes:

• Confusing MLflow with model building libraries
• Thinking MLflow is only for visualization
• Assuming MLflow deploys models directly

2. Which MLflow function is used to start a new experiment run in Python?

easy

A. mlflow.init_experiment()

B. mlflow.start_run()

C. mlflow.create_run()

D. mlflow.begin_experiment()

Solution

1. Step 1: Recall MLflow run start syntax

   The correct function to start a run is mlflow.start_run().

2. Step 2: Check other options

   Functions like init_experiment, create_run, and begin_experiment do not exist in MLflow API.

3. Final Answer:

   mlflow.start_run() -> Option B

4. Quick Check:

   Start run = mlflow.start_run() [OK]

Hint: Use start_run() to begin tracking an experiment run [OK]

Common Mistakes:

• Using non-existent MLflow functions
• Confusing experiment and run functions
• Misspelling function names

3. What will be the output of this MLflow code snippet?

import mlflow
with mlflow.start_run():
    mlflow.log_param('alpha', 0.1)
    mlflow.log_metric('accuracy', 0.95)
    run_info = mlflow.active_run().info
print(run_info.run_id is not None)

medium

A. True

B. False

C. None

D. Error

Solution

1. Step 1: Understand mlflow.start_run() context

   The code starts a run, logs parameters and metrics, then gets the active run info.

2. Step 2: Check run_id existence

   Inside the run context, run_id is assigned and not None, so print(run_info.run_id is not None) outputs True.

3. Final Answer:

   True -> Option A

4. Quick Check:

   Active run has run_id = True [OK]

Hint: Active run always has a run_id during context [OK]

Common Mistakes:

• Assuming run_id is None before logging
• Confusing run info with experiment info
• Expecting print to show run_id string

4. Identify the error in this MLflow code snippet:

import mlflow
mlflow.log_param('learning_rate', 0.01)
with mlflow.start_run():
    mlflow.log_metric('loss', 0.2)

medium

A. log_param called outside a run context

B. start_run() missing parentheses

C. log_metric called before log_param

D. No error, code runs fine

Solution

1. Step 1: Check order of MLflow calls

   log_param is called before starting a run, which is not allowed.

2. Step 2: Validate run context requirement

   MLflow requires logging functions inside a run context started by start_run().

3. Final Answer:

   log_param called outside a run context -> Option A

4. Quick Check:

   Logging outside run = error [OK]

Hint: Always log params and metrics inside start_run() [OK]

Common Mistakes:

• Calling log_param before start_run()
• Ignoring run context for logging
• Assuming log_metric order matters

5. You want to compare two ML models' performance using MLflow. Which steps correctly describe this process?

hard

A. Only log parameters for both models, metrics are not needed for comparison

B. Log both models' metrics in the same run, then compare metrics manually

C. Use mlflow.log_artifact() to save models, no need to log metrics or parameters

D. Run each model in separate mlflow.start_run() blocks, log metrics, then use MLflow UI to compare

Solution

1. Step 1: Understand MLflow run separation

   Each model should be run and logged in its own mlflow.start_run() block to keep results separate.

2. Step 2: Use MLflow UI for comparison

   After logging metrics and parameters, MLflow UI allows easy comparison of runs.

3. Final Answer:

   Run each model in separate mlflow.start_run() blocks, log metrics, then use MLflow UI to compare -> Option D

4. Quick Check:

   Separate runs + UI = compare models [OK]

Hint: Use separate runs and MLflow UI to compare models easily [OK]

Common Mistakes:

• Logging multiple models in one run
• Skipping metric logging
• Ignoring MLflow UI for comparison