Iterate over a python sequence in multiples of n?

A generator function would be neat:

def batch_gen(data, batch_size):
    for i in range(0, len(data), batch_size):
            yield data[i:i+batch_size]

Example use:

a = "abcdef"
for i in batch_gen(a, 2): print i

prints:

ab
cd
ef

I've got an alternative approach, that works for iterables that don't have a known length.

   
def groupsgen(seq, size):
    it = iter(seq)
    while True:
        values = ()        
        for n in xrange(size):
            values += (it.next(),)        
        yield values    

It works by iterating over the sequence (or other iterator) in groups of size, collecting the values in a tuple. At the end of each group, it yield the tuple.

When the iterator runs out of values, it produces a StopIteration exception which is then propagated up, indicating that groupsgen is out of values.

It assumes that the values come in sets of size (sets of 2, 3, etc). If not, any values left over are just discarded.

Don't forget about the zip() function:

a = 'abcdef'
for x,y in zip(a[::2], a[1::2]):
  print '%s%s' % (x,y)

I am sure someone is going to come up with some more "Pythonic" but how about:

for y in range(0, len(x), 2):
    print "%s%s" % (x[y], x[y+1])

Note that this would only work if you know that len(x) % 2 == 0;