yield from: The Extend Method for Generators

As Trey Hunner said: “The yield from statement is to a list.extend() the way a yield statement is to a list.append().”

Basic Usage

def my_generator():
    yield 1
    yield 2
    yield from [3, 4, 5]
    yield 6

gen = my_generator()
print(list(gen))  # Output: [1, 2, 3, 4, 5, 6]

In this example, yield from [3, 4, 5] is equivalent to:

for item in [3, 4, 5]:
    yield item

Example: Deep-Flattening Nested Iterables

from collections.abc import Iterable
from typing import Any, Iterator


def deep_flatten(iterable: Iterable) -> Iterator[Any]:
    """Flatten an iterable of iterables."""
    for element in iterable:
        # Handle strings as special case, since they are iterable
        if isinstance(element, str):
            yield element
        # Recursively flatten nested iterables
        elif isinstance(element, Iterable):
            yield from deep_flatten(element)
        # Base case: yield non-iterable elements
        else:
            yield element

References:

• Python Morsels by Trey Hunner