batch_iterator.py

import itertools

def grouper(iterable, n, fillvalue=None):
    """Collect data into fixed-length chunks or blocks"""
    # grouper('ABCDEFG', 3, 'x') --> ABC DEF Gxx
    args = [iter(iterable)] * n
    return itertools.zip_longest(*args, fillvalue=fillvalue)
    
a=itertools.chain.from_iterable(itertools.repeat(['a', 'b', 'c'], 4))
b=itertools.chain.from_iterable(itertools.repeat(['d', 'e', 'f', 'g'], 3))
for pa, pb in zip(grouper(a, 2), grouper(b, 2)):
    print(pa, pb, [str(qt) for qt in zip(pa, pb)])
    print('==')
"""
output:

('a', 'b') ('d', 'e') ["('a', 'd')", "('b', 'e')"]
==
('c', 'a') ('f', 'g') ["('c', 'f')", "('a', 'g')"]
==
('b', 'c') ('d', 'e') ["('b', 'd')", "('c', 'e')"]
==
('a', 'b') ('f', 'g') ["('a', 'f')", "('b', 'g')"]
==
('c', 'a') ('d', 'e') ["('c', 'd')", "('a', 'e')"]
==
('b', 'c') ('f', 'g') ["('b', 'f')", "('c', 'g')"]
==
"""