Installing MLflow

MLflow can be installed by running

pip install mlflow


You cannot install MLflow on the MacOS system installation of Python. We recommend installing Python 3 through the Homebrew package manager using brew install python. (In this case, installing mlflow is now pip3 install mlflow).

At this point we recommend you follow the Tutorial for a walk-through on how you can leverage MLflow in your daily workflow.

Using the Tracking API

The MLflow Tracking API lets you log metrics and artifacts (files) from your data science code and see a history of your runs. You can try it out by writing a simple Python script as follows (this example is also included in example/quickstart/test.py):

import os
from mlflow import log_metric, log_param, log_artifact

if __name__ == "__main__":
    # Log a parameter (key-value pair)
    log_param("param1", 5)

    # Log a metric; metrics can be updated throughout the run
    log_metric("foo", 1)
    log_metric("foo", 2)
    log_metric("foo", 3)

    # Log an artifact (output file)
    with open("output.txt", "w") as f:
        f.write("Hello world!")

Viewing the Tracking UI

By default, wherever you run your program, the tracking API writes data into files into an mlruns directory. You can then run MLflow’s Tracking UI:

mlflow ui

and view it at http://localhost:5000.

Alternatively, you can configure MLflow to log runs to a remote server to manage your results centrally or share them across a team.

Running MLflow Projects

MLflow allows you to package code and its dependencies as a project that can be run in a reproducible fashion on other data. Each project includes its code and a MLproject file that defines its dependencies (for example, Python environment) as well as what commands can be run into the project and what arguments they take.

You can easily run existing projects with the mlflow run command, which runs a project from either a local directory or a GitHub URI:

mlflow run example/tutorial -P alpha=0.5

mlflow run git@github.com:databricks/mlflow-example.git -P alpha=5

There’s a sample project in example/tutorial, including a MLproject file that specifies its dependencies. All projects that run also log their Tracking API data in the local mlruns directory (or on your tracking server if you’ve configured one), so you should be able to see these runs using mlflow ui.


By default mlflow run installs all dependencies using conda. To run a project without using conda, you can provide the --no-conda option to mlflow run. In this case, you must ensure that the necessary dependencies are already installed in your Python environment.

For more information, see MLflow Projects.

Saving and Serving Models

MLflow includes a generic MLmodel format for saving models from a variety of tools in diverse flavors. For example, many models can be served as Python functions, so an MLmodel file can declare how each model should be interpreted as a Python function in order to let various tools serve it. MLflow also includes tools for running such models locally and exporting them to Docker containers or commercial serving platforms.

To illustrate this functionality, the mlflow.sklearn package can log scikit-learn models as MLflow artifacts and then load them again for serving. There is an example training application in example/quickstart/test_sklearn.py that you can run as follows:

python example/quickstart/test_sklearn.py

When you run the example, it outputs an MLflow run ID for that experiment. If you look at mlflow ui, you will also see that the run saved a model folder containing an MLmodel description file and a pickled scikit-learn model. You can pass the run ID and the path of the model within the artifacts directory (here “model”) to various tools. For example, MLflow includes a simple REST server for scikit-learn models:

mlflow sklearn serve -r <RUN_ID> model


By default the server will run on port 5000. If it is already in use the –port option to specify a different port. For example mlflow sklearn serve --port 1234 -r <RUN_ID> model

Once you have started the server, you can pass it some sample data with curl and see the predictions:

curl -d '[{"x": 1}, {"x": -1}]' -H 'Content-Type: application/json' -X POST localhost:5000/invocations

which returns:

{"predictions": [1, 0]}


The example/quickstart/test_sklearn.py script must be run with the same Python version as the version of Python which runs mlflow sklearn serve. If they are not the same version, a stacktrace below may appear:

File "/usr/local/lib/python3.6/site-packages/mlflow/sklearn.py", line 54, in _load_model_from_local_file
return pickle.load(f)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc6 in position 0: ordinal not in range(128)

For more information, see MLflow Models.