Is there a shorthand syntax for a sequence of throwaway variables?

Question

Let\'s say you have a situation like this:

_, _, _, substring_1, _, substring_2 = some_string.split(\',\')

Is there a shorthand way of expressi

Answer 1

You could just use str.rsplit with a limit:

>>> s = 'a,b,c,d,e,f'
>>> s.rsplit(',', 3)  # i.e. split on at most three commas, from the right
['a,b,c', 'd', 'e', 'f']
>>> _, d, _, f = s.rsplit(',', 3)
>>> d
'd'
>>> f
'f'

---

If you upgrade to Python 3.x, you can use *_ to absorb an arbitrary number of elements (you'll get a SyntaxError in 2.x, though):

>>> *_, d, _, f = s.split(',')
>>> d
'd'
>>> f
'f'

Answer 2

Yes, if you are using Python 3 and you don't care if there are more or less than 3 entries before the last 3:

*_, first, _, second = somestring.split(',')

Otherwise, if you want the last 3 elements (regardless of how many entries the string has) you can use str.rsplit as Jon points out:

_, first, _, second = s.rsplit(',', 3)

If you want the 3rd and the 5th elements (regardless of how many elements the string has) you can use chepner's answer:

from operator import itemgetter

extract = itemgetter(3, 5)
first, second = extract(s.split(','))

Finally, if there must be six entries in the string, your best bet is to be explicit:

KeyFields = namedtuple('KeyFields', 'first second')

def extract_key_fields(s):
    data = s.split(",")
    if len(data) != 6:
        raise ValueError("Must provide six fields")
    return KeyFields(data[3], data[5])

key_fields = extract_key_fields(somestring)
key_fields.first   # d
key_fields.second  # f

Answer 3

Not a syntactic shortcut, but you might want to use the itemgetter function from the operator module:

from operator import itemgetter
my_pair = itemgetter(3, 5)
substring_1, substring_2 = my_pair(some_string.split(','))

Or, define my_pair to wrap the call to split as well:

def my_pair(x):
    return itemgetter(3,5)(x.split(','))

substring_1, substring_2 = my_pair(some_string)