拿一片发电机

Itertoolsislice 允许你切割发电机：

results = fetch_paged_results()  # returns a generator
limit = 20  # Only want the first 20 results
for data in itertools.islice(results, limit):
    print(data)

通常你不能切割发电机：

def gen():
    n = 0
    while n < 20:
        n += 1
        yield n

for part in gen()[:3]:
    print(part)

会给

Traceback (most recent call last):
  File "gen.py", line 6, in <module>
    for part in gen()[:3]:
TypeError: 'generator' object is not subscriptable

但是，这有效：

import itertools

def gen():
    n = 0
    while n < 20:
        n += 1
        yield n

for part in itertools.islice(gen(), 3):
    print(part)

请注意，像常规切片一样，你也可以使用 start，stop 和 step 参数：

itertools.islice(iterable, 1, 30, 3)