# Source code for monty.itertools

```# coding: utf-8
from __future__ import absolute_import, print_function, division

import itertools

[docs]def chunks(items, n):
"""
Yield successive n-sized chunks from a list-like object.

>>> import pprint
>>> pprint.pprint(list(chunks(range(1, 25), 10)))
[(1, 2, 3, 4, 5, 6, 7, 8, 9, 10),
(11, 12, 13, 14, 15, 16, 17, 18, 19, 20),
(21, 22, 23, 24)]
"""
it = iter(items)
chunk = tuple(itertools.islice(it, n))
while chunk:
yield chunk
chunk = tuple(itertools.islice(it, n))

[docs]def iterator_from_slice(s):
"""
Constructs an iterator given a slice object s.

.. note::

The function returns an infinite iterator if s.stop is None
"""
import numpy as np
start = s.start if s.start is not None else 0
step = s.step if s.step is not None else 1

if s.stop is None:
# Infinite iterator.
return itertools.count(start=start, step=step)
else:
# xrange-like iterator that supports float.
return iter(np.arange(start, s.stop, step))

[docs]def iuptri(items, diago=True, with_inds=False):
"""
A generator that yields the upper triangle of the matrix (items x items)

Args:
items: Iterable object with elements [e0, e1, ...]
diago: False if diagonal matrix elements should be excluded
with_inds: If True, (i,j) (e_i, e_j) is returned else (e_i, e_j)

>>> for (ij, mate) in iuptri([0,1], with_inds=True):
...     print("ij:", ij, "mate:", mate)
ij: (0, 0) mate: (0, 0)
ij: (0, 1) mate: (0, 1)
ij: (1, 1) mate: (1, 1)
"""
for (ii, item1) in enumerate(items):
for (jj, item2) in enumerate(items):
do_yield = (jj >= ii) if diago else (jj > ii)
if do_yield:
if with_inds:
yield (ii, jj), (item1, item2)
else:
yield item1, item2

[docs]def ilotri(items, diago=True, with_inds=False):
"""
A generator that yields the lower triangle of the matrix (items x items)

Args:
items: Iterable object with elements [e0, e1, ...]
diago: False if diagonal matrix elements should be excluded
with_inds: If True, (i,j) (e_i, e_j) is returned else (e_i, e_j)

>>> for (ij, mate) in ilotri([0,1], with_inds=True):
...     print("ij:", ij, "mate:", mate)
ij: (0, 0) mate: (0, 0)
ij: (1, 0) mate: (1, 0)
ij: (1, 1) mate: (1, 1)
"""
for (ii, item1) in enumerate(items):
for (jj, item2) in enumerate(items):
do_yield = (jj <= ii) if diago else (jj < ii)
if do_yield:
if with_inds:
yield (ii, jj), (item1, item2)
else:
yield item1, item2
```