unpack_fields

This decorator works on a function that outputs a tuple and unpacks its elements to make them individually available for consumption. Essentially, it expands the original function into n separate functions, each of which takes the original output tuple and, in return, outputs a specific field based on the index supplied to the unpack_fields decorator.

import pandas as pd
from hamilton.function_modifiers import unpack_fields

@unpack_fields('X_train', 'X_test', 'y_train', 'y_test')
def train_test_split_func(
    feature_matrix: np.ndarray,
    target: np.ndarray,
    test_size_fraction: float,
    shuffle_train_test_split: bool,
) -> Tuple[np.ndarray, np.ndarray, np.ndarray, np.ndarray]:
    ...  # Calculate the train-test split
    return X_train, X_test, y_train, y_test

The arguments to the decorator not only represent the names of the resulting fields but also determine their position in the output tuple. This means you can choose to unpack a subset of the fields or declare an indeterminate number of fields — as long as the number of requested fields does not exceed the number of elements in the output tuple.

import pandas as pd
from hamilton.function_modifiers import unpack_fields

@unpack_fields('X_train', 'X_test', 'y_train', 'y_test')
def train_test_split_func(
    feature_matrix: np.ndarray,
    target: np.ndarray,
    test_size_fraction: float,
    shuffle_train_test_split: bool,
) -> Tuple[np.ndarray, ...]:  # indeterminate number of fields
    ...  # Calculate the train-test split
    return X_train, X_test, y_train, y_test

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Reference Documentation

class hamilton.function_modifiers.unpack_fields(*fields: str)

Unpacks fields from a tuple output.

Expands a single function into the following nodes:

• 1 function that outputs the original tuple

• n functions, each of which take in the original tuple and output a specific field

The decorated function must have an return type of either tuple (python 3.9+) or typing.Tuple, and must specify either: - An explicit length tuple (e.g.`tuple[int, str]`, typing.Tuple[int, str]) - An indeterminate length tuple (e.g. tuple[int, …], typing.Tuple[int, …])

Parameters:

fields – Fields to unpack from the return value of the decorated function.

__init__(*fields: str)

Initializes the node transformer to only allow a single node to be transformed. Note this passes target=None to the superclass, which means that it will only apply to the ‘sink’ nodes produced.