Choose Key Parameters

Use all parameters (the default)

Omit key= to use every parameter as part of the key:

@stet.once
def run_experiment(alpha, seed, n_iter=1000):
    ...

Use this when every parameter genuinely changes the result.

Specify key parameters explicitly

Use key= to exclude parameters that don't define the experiment, for example computational settings like n_iter, batch_size, or verbose:

@stet.once(key=['alpha', 'seed'])
def run_experiment(alpha, seed, n_iter=1000):
    ...

Now only alpha and seed determine whether a run is skipped, regardless of n_iter.

Exclude parameters with default values from the key

If a parameter has a default value and you call the function both with and without it, the two calls will be treated as different runs unless you exclude it from the key:

# without key=, these are different runs:
run_experiment(alpha=0.1, seed=1)              # n_iter=1000 (default)
run_experiment(alpha=0.1, seed=1, n_iter=500)  # n_iter=500

# with key=['alpha', 'seed'], both are the same run:
run_experiment(alpha=0.1, seed=1)
run_experiment(alpha=0.1, seed=1, n_iter=500)  # skipped

See How stet Works for a fuller discussion of how parameter identity is determined.