mitosis

Reproduce Machine Learning experiments easily

A package designed to manage and visualize experiments, tracking changes across different commits, parameterizations, and random seed.

Trivial Example

Hypothesis: the maximum value of a sine wave is equal to its amplitude.

sine_experiment/__init__.py

import numpy as np

name = "sine-exp"
lookup_dict = {"frequency": {"fast": 10, "slow": 1}}

def run(amplitude, frequency):
    """Deterimne if the maximum value of the sine function equals ``amplitude``"""
    x = np.arange(0, 10, .05)
    y = amplitude * np.sin(frequency * x)
    err = np.abs(max(y) - amplitude)
    return {"main": err}

Commit these changes to a repository. After installing sine_experiment as a python package, in CLI, run:

mitosis -m sine_experiment --param frequency=slow --eval-param amplitude=4

Mitosis will run sin_experiment.run(), saving all output as an html file in the current directory. It will also track the parameters and results. If you later change the variant named "slow" to set frequency=2, mitosis will raise a RuntimeError, preventing you from running a trial. If you want to run sine_experiment with a different parameter value, you need to name that variant something new. Eval parameters, like "amplitude" in the example, behave differently. Rather than being specified by lookup_dict, they are evaluated directly.

How it Works

Behind the scenes:

The first time mitosis.run() is passed a new experiment, it takes several actions:

1. Create a database for your experiment in trials_folder
2. Add a table to track all of the experiment trials
3. Add tables to track all of the different variants of your experiment.
4. Create a folder for the trial to store metadata.
5. Create and run a jupyter notebook in memory, saving the result as an HTML file
6. Updating the database of all trials with the results of the experiment.
7. Save experiment config of parameters actually created by jupyter notebook (in metadata folder)
8. Save a freezefile of python packages installed (in metadata folder)
9. Save the experiments results (in metadata folder)

In step 3, mitosis attempts to create a unique and reproduceable string from each parameter value. This is essential, since it strikes at the heart of what reproducibility means when talking about experiments. It's also hard, since most python objects are mutable and/or have their id() stored in their string representation. So lists must be sorted, dicts must be ordered, and function and method arguments must have their __str__() attribute replaced. This is imperfectly done, see the **Reproduceability ** section for comments on the edge cases where mitosis will either treat the same parameter as a new variant, or treat two different parameters as having the same value.

In step 5, mitosis needs to start the jupyter notebook with the appropriate variables. Instead of sending the variables to the notebook, the notebook re-evaluates eval parameters and re-looks up lookup parameters. Previously, parameters were sent to the notebook via pickle; that proved fragile.

The next time mitosis.run() is given the same experiment, it will

1. Determine whether parameter names and values match parameters in a previously established variant. It will either:
   • Reject the trial if the passed variant names match existing variants but with different values.
   • Create a new variant for the parameter.
2. Proceeds through steps 4 to 9 above.

Abstractions

Experiment: the definition of a procedure that will test a hypothesis. As a python object, an experiment is a series of steps, each of which is a tuple of a name, a lookup dictionary, and a Callable that takes any number of arguments and returns a dict with at least a key named "main". All but the last also need a key "data" to pass to the next step. All but the first step need to accept an argument named data.

In its current form, mitosis does not require a hypothesis, but consider the "main" metric to stand in for a more formal hypothesis (though a user can always define an experiment that sets the main metric to a constant).

When running in module mode (-m on command line), the lookup dictionary, name, and callable are all loaded from the module's lookup_dict, __qualname__, and run variables. Otherwise, they're configured in pyproject.toml.

Parameter: An argument to an experiment. These are the axes by which an experiment step may vary, e.g. sim_params, data_params, solver_params... etc. When this argument is a Collection, sometimes the singular (parameter) and plural (parameters) are used interchangeably. Parameters can either be lookup parameters (which use the step's' lookup_dict) or eval parameters (which are typically simple evaluations, e.g. setting the random seed to a given integer). Eval parameters which are strings need quotes.

When running in module mode (-m on command line), experiments only have a single step, so mitosis associates all arguments with that step. In normal mode, the arguments for a step must be prefixed with that step name, e.g. step1.noise_level

Variant: An experimental parameter assigned to specific values and given a name.

Trial: a single run of an experiment with all variants specified. Within mitosis, the name of a trial is the experiment name, concatenated with variant names for each argument, and suffixed by the number of times that particular trial has been run. E.g. If an experiment has three arguments, the first trial run could be called "trial_sine-arg1a-arg2test-arg3foo-1" If a bugfix is committed to the experiment and the trial re-run with the same parameters, the new trial would be named "trial_sine-arg1a-arg2test-arg3foo-2".

Within mitosis, the trial is used to name the resulting html file and is stored in the "variant" and "iteration" columns in the experiment's sqlite database. the pseudorandom key that is attached to filename serves as an effective primary key over all variants and trials.

API

Mitosis is primarily intended as a command line program, so mitosis --help has the syntax documentation. There is only one intentionally publi part of the api: mitosis.load_trial_data().

Here's a pre-0.5.0 example, when the -m flag was assumed. For 0.5.0 usage, see the section on "More advanced usage"

Untracked parameters

If there are certain parameters that are not worth tracking, e.g. plotting flags that do not change the mathematical results, prepend the argument name with "+". An example:

mitosis -m project_pkg.exp1 -e +plot=True -p +plot_axes=dense

Fast iterations: Debug

Debug is straightforwards: mitosis project_pkg.exp1 -d ... runs in debug mode. This arg allows you to run experiments in a dirty git repository (or no repository) and will neither save results in the experimental database, nor increment the trials counter, nor verify/lock in the definitions of any variants. It will, however, create the output notebook.

Early experiment prototyping involves quickly iterating on parameter lists and complexity. mitosis will still lock in definitions of variants, which means that you will likely go through variant names quickly. This disambiguation is somewhat intentional, but you can free up names by deleting or renaming the experiment database or deleting records in the variant_param_name table.

Mitosis also sets the log level of the experiment module to INFO and gives it a FileHandler to the metadata directory. In Debug mode, mitosis sets the log level of the experiment to DEBUG.

More advanced usage.

Module-style experiments

It should be noted that mitosis only works on installed packages - modules that you can run using python -m pkgname.modname.

When you want two modules share the same, long lookup_dict, I have found creating a module with multiple dictionaries works well, e.g.

project_pkg/
    |-- __init__.py     # Should look like
    |                   param_1 = {"var1": 1, "var2": 2}
    |                   param_2 = {"foo": "hello", "bar": "world"}
    |
    |                   # Each experiment gets same lookup dict
    |-- exp1.py         lookup_dict = vars(project_pkg)
    |-- exp2.py         lookup_dict = vars(project_pkg)

This way, the same variants can be used for different experiemnts:

mitosis -m project_pkg.exp1 -e seed=2 -p param_1=var_1 -p param_2=foo
mitosis -m project_pkg.exp2 -e seed=2 -p param_1=var_1 -p param_2=foo

It is also common to have one experiment wrap another, e.g. if exp2 is a gridsearch around exp1.

Recommended: multi-step experiments

Sometimes it's useful to combine steps from different packages, or share steps across projects, or distribute your experiment without the clutter of a lookup dictionary holding every variant you tried out. In these cases, the project is responsible for naming and connecting the callable <-> lookup-dictionary association. These experiment steps are specified in pyproject.toml, in the [tools.mitosis.steps] table using object reference notation (à la plugins).

Let's say your project folder is called my_paper and contains an eponymous python package. You have an experiment defined in the package first_exp, broken down into functions make_data() and linear_pipeline, but you want to be able to swap out the first step for real data in another module geospatial.datasets, you could have the following table in your project's pyproject.toml (likely within the my_paper repo):

[tool.mitosis.steps]
real_data = ["geospatial.datasets:load_data", "my_paper:data_config"]
sim_data = ["first_exp:make_data", "my_paper:data_config"]
fit_eval = ["first_exp:linear_pipeline", "my_paper:meth_config"]

This also says that the lookup dicts for each step are all imported from my_paper. You would invoke experiments like:

mitosis sim_data fit_eval -p sim_data.noise=low -e fit_eval.alpha=.5
mitosis real_data fit_eval -p real_data.file="oct-2024.hd5" -e fit_eval.alpha=.5

Needless to say, all of the callables need to pass data compatibly, e.g. first_exp.linear_pipeline(first_exp.make_data(...)["data"], ...) must make sense, as must first_exp.linear_pipeline(geospatial.datasets.load_data(...)["data"], ...). Some caution here is advised - mitosis does not yet check all editably-installed packages for being git-clean.

You could then have code in my_paper that loads the data from these trials and builds comparison plots, or you could rely on the plots each experiment creates. You could also have a shell/batch script that spawns the main experiments of your paper.

I'm often on a server and want to disconnect while the experiment is running, so I wrap my experiments in nohup ... &> exp1.log &.

pyproject.toml config

The [tool.mitosis] table can be used to set trials-folder. If relative, it is relative to repository root.

Using persistent data

There are two obviously useful things to do after an experiment:

• view the html file. python -m http.server is helpful to browse results
• load the data with load_trial_data()

Beyond this, the metadata mitosis keeps to disk is useful for troubleshooting or reproducing experiments, but no facility yet exists to browse or compare experiments.