Local Training and Prediction#

In Binding a Model and Dataset together, we defined a Model and Dataset object, bound them together, and defined the core functions needed for model training and prediction.

In this guide, we’ll learn how to interact with these objects locally to ensure that our code is working as expected.


Local interaction with Model objects are mainly useful for local development, debugging, and unit testing of your UnionML app.

Here’s our complete UnionML app for digit classification in a app.py script:

from typing import List

import pandas as pd
from sklearn.datasets import load_digits
from sklearn.linear_model import LogisticRegression
from sklearn.metrics import accuracy_score

from unionml import Dataset, Model

dataset = Dataset(name="digits_dataset", test_size=0.2, shuffle=True, targets=["target"])
model = Model(name="digits_classifier", init=LogisticRegression, dataset=dataset)

def reader(sample_frac: float = 1.0, random_state: int = 12345) -> pd.DataFrame:
    data = load_digits(as_frame=True).frame
    return data.sample(frac=sample_frac, random_state=random_state)

def trainer(estimator: LogisticRegression, features: pd.DataFrame, target: pd.DataFrame) -> LogisticRegression:
    return estimator.fit(features, target.squeeze())

def predictor(estimator: LogisticRegression, features: pd.DataFrame) -> List[float]:
    return [float(x) for x in estimator.predict(features)]

def evaluator(estimator: LogisticRegression, features: pd.DataFrame, target: pd.DataFrame) -> float:
    return float(accuracy_score(target.squeeze(), predictor(estimator, features)))
/home/docs/checkouts/readthedocs.org/user_builds/unionml/envs/stable/lib/python3.8/site-packages/tqdm/auto.py:22: TqdmWarning: IProgress not found. Please update jupyter and ipywidgets. See https://ipywidgets.readthedocs.io/en/stable/user_install.html
  from .autonotebook import tqdm as notebook_tqdm

Execute as a Python Module#

We can then invoke the model.train method to train the sklearn estimator and model.predict to generate predictions. Then invoke the app script with python app.py:

if __name__ == "__main__":
    model_object, metrics = model.train(
        hyperparameters={"C": 1.0, "max_iter": 10000},

    predictions = model.predict(
        features=load_digits(as_frame=True).frame.sample(5, random_state=42)

    print(f"model object: {model_object}")
    print(f"training metrics: {metrics}")
    print(f"predictions: {predictions}")

    # save model to a file, using joblib as the default serialization format
model object: LogisticRegression(max_iter=10000)
training metrics: {'train': 1.0, 'test': 0.9694444444444444}
predictions: [6.0, 9.0, 3.0, 7.0, 2.0]


You may notice a few things about the code example above:

  • The model.train method takes the dataset.reader arguments as keyword-only arguments. In this case, the sample_frac and random_state values are passed into model.train and forwarded to dataset.reader.

  • model.train returns a model instance and a dictionary of metrics.

    • The model instance is the same type as the return annotation of the model.trainer function, which in this case is LogisticRegression.

    • The metrics dictionary maps dataset split keys {"train", "test"} to metrics of the same type as the return annotation of the model.evaluator, which in this case is a float.

  • The model.predict method accepts a features keyword argument containing the features of the same type defined in the model.predictor function.

  • At the end of the file we save the model object to a file called /tmp/model_object.joblib. This is simply an sklearn base estimator that you know and love!

Serve with FastAPI#

UnionML integrates with FastAPI to make model serving super easy. Simply create a FastAPI app and pass it into model.serve in the app.py script:

from fastapi import FastAPI

# dataset and model definition

app = FastAPI()


model.serve will take the FastAPI app and automatically create a /predict/ endpoint that you can invoke with HTTP requests.

Start the server with unionml serve

unionml serve app:app --model-path /tmp/model_object.joblib --reload


The --model-path option points to a local file containing the serialized model object that we created above when we executed the UnionML app script.

Once the server’s started, you can use the Python requests library or any other HTTP library to get predictions from input features. For example, you can copy the following code into a client.py script to generate predictions from the endpoint:

import requests

# generate predictions
    json={"features": load_digits(as_frame=True).frame.sample(5, random_state=42).to_dict(orient="records")},


The /predict endpoint computation is being done on the app server itself, which, in this case, is probably your laptop 💻. You’ll need to ensure that your prediction server has the resources needed to load the model into memory and generate predictions.


We’ve run our training and prediction code by invoking our UnionML app as a python module and starting a local FastAPI server, but how do we deploy it as a suite of integrated machine learning services in the ☁️ cloud?

UnionML is coupled with Flyte, which is a scalable, reliable, and robust orchestration platform for data processing and machine learning. But before we deploy to the cloud, it’s important to understand what a Flyte cluster is by spinning up a Flyte Cluster locally.