yield from und Delegation

Das Problem, das yield from löst

def manual():
    for x in [1, 2, 3]:
        yield x

print(list(manual()))

yield from kennenlernen

def delegate():
    yield from [1, 2, 3]

print(list(delegate()))

Mehrere Quellen kombinieren

def chained():
    yield from 'ab'
    yield from [1, 2]
    yield from range(2)

print(list(chained()))

An einen anderen Generator delegieren

def evens(n):
    for i in range(n):
        if i % 2 == 0:
            yield i

def report(n):
    print('evens:')
    yield from evens(n)

print(list(report(6)))

Verschachtelte Listen abflachen

def flatten(items):
    for item in items:
        if isinstance(item, list):
            yield from flatten(item)
        else:
            yield item

print(list(flatten([1, [2, [3, 4]], 5])))

yield from im Vergleich zu einer Schleife

def with_loop(src):
    for x in src:
        yield x

def with_yield_from(src):
    yield from src

print(list(with_loop(range(3))))
print(list(with_yield_from(range(3))))

Den Rückgabewert eines Untergenerators erfassen

def counter(n):
    count = 0
    for i in range(n):
        yield i
        count += 1
    return count

def driver():
    total = yield from counter(3)
    print('subgen yielded', total, 'items')

list(driver())

Eine Pipeline erstellen

def source():
    yield from range(5)

def only_odd(src):
    for x in src:
        if x % 2 == 1:
            yield x

def pipeline():
    yield from only_odd(source())

print(list(pipeline()))

An jedes Iterable delegieren

def mixed():
    yield from {1, 2, 3}
    yield from ('a', 'b')

result = list(mixed())
print(sorted(str(x) for x in result))

Generatoren in der richtigen Reihenfolge zusammenführen

def concat(*iterables):
    for it in iterables:
        yield from it

print(list(concat([1, 2], [3], [4, 5])))

Bessere Lesbarkeit

def walk(tree):
    yield tree['name']
    for child in tree.get('children', []):
        yield from walk(child)

tree = {'name': 'root', 'children': [
    {'name': 'a'},
    {'name': 'b', 'children': [{'name': 'c'}]}
]}
print(list(walk(tree)))

Kurzer Test

Zusammenfassung