Converting a list into comma-separated string with “and” before the last item - Python 2.7

Question

I have created this function to parse the list:

listy = [\'item1\', \'item2\',\'item3\',\'item4\',\'item5\', \'item6\']


def coma(abc):
    for i in abc[0:-         


        

Answer 1

In python, many functions, that work with lists also works with iterators (like join, sum, list). To get the last item of a iterable is not that easy, because you cannot get the length, because it may be unknown in advance.

def coma_iter(iterable):
    sep = ''
    last = None
    for next in iterable:
        if last is not None:
            yield sep
            yield last
            sep = ', '
        last = next
    if sep:
        yield ', and '
    if last is not None:
        yield last

print ''.join(coma_iter(listy))

Answer 2

When there are 1+ items in the list (if not, just use the first element):

>>> "{} and {}".format(", ".join(listy[:-1]),  listy[-1])
'item1, item2, item3, item4, item5, and item6'

Edit: If you need an Oxford comma (didn't know it even existed!) -- just use: ", and" isntead.

Answer 3

It's generally bad practice to use + when combining strings, as it is generally slow. Instead, you can use

def comma(items):
    return "{}, and {}".format(", ".join(items[:-1]), items[-1])

You should note, however, that this will break if you only have one item:

>>> comma(["spam"])
', and spam'

To solve that, you can either test the length of the list (if len(items) >= 2:), or do this, which (imho) is slightly more pythonic:

def comma(items):
    start, last = items[:-1], items[-1]

    if start:
        return "{}, and {}".format(", ".join(start), last)
    else:
        return last

As we saw above, a single item list will result in an empty value for items[:-1]. if last: is just a pythonic way of checking if last is empty.

Answer 4

def oxford_comma_join(l):
    if not l:
        return ""
    elif len(l) == 1:
        return l[0]
    else:
        return ', '.join(l[:-1]) + ", and " + l[-1]

print(oxford_comma_join(['item1', 'item2', 'item3', 'item4', 'item5', 'item6']))

Output:

item1, item2, item3, item4, item5, and item6

Also as an aside the Pythonic way to write

for i in abc[0:-1]:

is

for i in abc[:-1]:

Answer 5

You can also try the quoter library

>>> import quoter
>>> mylist = ['a', 'b', 'c']
>>> quoter.and_join(mylist)
'a, b, and c'
>>> quoter.or_join(mylist)
'a, b, or c'

https://pypi.python.org/pypi/quoter

Answer 6

def coma(lst):
    return '{} and {}'.format(', '.join(lst[:-1]), lst[-1])