Yield each iterable item along with the item before it

with_previous.py

def couple(iterable, *, first=None):
    """Yield each iterable item along with the item before it."""
    prev = first
    for item in iterable:
        yield prev, item
        prev = item

# >>> list(couple(range(5)))
# >>> [(None, 0), (0, 1), (1, 2), (2, 3), (3, 4)]
# >>> list(couple(range(5), first=10))
# >>> [(10, 0), (0, 1), (1, 2), (2, 3), (3, 4)]

it also shows how to use * for requiring keyword-only arguments without capturing unlimited positional arguments. So, no call like this allowed.

couple(range(5), 10)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-70-13870c826a4b> in <module>
----> 1 list(couple(range(5), 10))

TypeError: couple() takes 1 positional argument but 2 were given