可迭代对象按固定大小chunk分割，不补齐

batch.py

from itertools import islice, chain

#!/usr/bin/python3
def batch(iterable, size):
    source_iter = iter(iterable)
    while True:
        batch_iter = islice(source_iter, size)
        try:
            first_element = next(batch_iter)
        except StopIteration:
            return
        yield chain([first_element], batch_iter)
        
        
# In [42]: for r in batch([1,2,3], 2):
#    ...:     print(list(r))
#[1, 2]
#[3]