Python Language Take a slice of a generator


Example

Itertools "islice" allows you to slice a generator:

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

Normally you cannot slice a generator:

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

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

Will give

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

However, this works:

import itertools

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

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

Note that like a regular slice, you can also use start, stop and step arguments:

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