iterate over mix of single values and iterables in python

Question

I'm writing a for loop in Python and I'd like to iterate over a mix of single objects and flattened lists (or tuples) of objects.

For example:

a = 'one'
b = 'two'
c = [4, 5]
d = (10, 20, 30)

I'd like to iterate over all of these in a for loop. I was thinking a syntax like this would be elegant:

for obj in what_goes_here(a, b, *c, *d):
  # do something with obj

I looked in itertools for what_goes_here and I didn't see anything, but I feel I must be missing something obvious!

The closest I found was chain but I'm wondering if anything exists that would leave my example unchanged (replacing what_goes_here only).

The problem you will have is that strings are iterable, so your strings are likely to get unbundled into single characters. I think you'll probably need to write your own function for this. — Tom Dalton, Jan 27 '16 at 23:06
```l = [a, b, c, d]``` ```list(itertools.chain(*[x if not isinstance(x, str) else [x] for x in l]))``` — Al Johri, Jan 27 '16 at 23:10
As what @AlJohri has in the list comprehension you could check for the objects type. — tijko, Jan 27 '16 at 23:12
@AlJohri: `isinstance(x, str)`? Doesn't work if `b = 12` right? — Remi Guan, Jan 27 '16 at 23:15
@KevinGuan he wants to replicate [a, b, *c, *d] without having to manually put asterisks everywhere — Al Johri, Jan 27 '16 at 23:22
@AlJohri: Did he say that? Where? I can only see a *but I'm wondering if anything exists that would leave my example unchanged (replacing what_goes_here only)*. — Remi Guan, Jan 27 '16 at 23:25
@AlJohri - I don't see anything about not wanting the asterisks there. In fact, the use of those asterisks to indicate what should and should not be unpacked is the reason this question isn't a duplicate of [this one](http://stackoverflow.com/questions/2158395/flatten-an-irregular-list-of-lists-in-python). — TigerhawkT3, Jan 27 '16 at 23:26

score 2 · Accepted Answer · answered Jan 27 '16 at 23:25

You can do this, but you have to use Python 3.5 or higher for the expanded unpacking syntax. Put all the arguments into a container (like a tuple) then send that container to itertools.chain.

>>> import itertools
>>> a = 'one'
>>> b = 'two'
>>> c = [4, 5]
>>> d = (10, 20, 30)
>>> list(itertools.chain((a, b, *c, *d)))
['one', 'two', 4, 5, 10, 20, 30]
>>> list(itertools.chain((a, *c, b, *d)))
['one', 4, 5, 'two', 10, 20, 30]
>>> list(itertools.chain((*a, *c, b, *d)))
['o', 'n', 'e', 4, 5, 'two', 10, 20, 30]

score 0 · Answer 2 · answered Jan 27 '16 at 23:20

0

import collections, itertools

a = 'one'
b = 'two'
c = [4, 5]
d = (10, 20, 30)
e = 12

l = [a, b, c, d, e]

newl = list(itertools.chain(*[x if isinstance(x, collections.Iterable) and not isinstance(x, str) else [x] for x in l]))

answered Jan 27 '16 at 23:20

Al Johri

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iterate over mix of single values and iterables in python

2 Answers2