Generatorausdrücke

Einführung

Syntax von Generatorausdrücken

gen = (x**2 for x in range(5))
print(gen)  # generator object
print(next(gen))  # 0
print(next(gen))  # 1

Speichereffizienz

total = sum(x**2 for x in range(100))
print(total)

Einen Generator verbrauchen

gen = (x for x in range(3))
for val in gen:
    print(val)
# gen is now exhausted

Generator als Funktionsargument

print(sum(x**2 for x in range(10)))
print(max(len(w) for w in ['cat', 'elephant', 'ant']))

Generatoren verketten

evens = (x for x in range(100) if x % 2 == 0)
big_evens = (x for x in evens if x > 50)
print(list(big_evens))

In Liste/Tupel umwandeln

gen = (x**2 for x in range(5))
print(list(gen))

Generatorausdruck im Vergleich zur List Comprehension

import sys
lst = [x**2 for x in range(1000)]
gen = (x**2 for x in range(1000))
print(sys.getsizeof(lst), sys.getsizeof(gen))

Unendliche Generatoren

import itertools
first10 = list(itertools.islice(itertools.count(0), 10))
print(first10)

any() und all() mit Generatoren

nums = [1, 3, 7, 2]
print(any(x > 5 for x in nums))
print(all(x > 0 for x in nums))

Pipelines

data = range(1000)
filtered = (x for x in data if x % 7 == 0)
transformed = (x * 2 for x in filtered)
print(sum(transformed))

Wissenscheck

Zusammenfassung

Weiter