List with duplicated values and suffix

You can use itertools.chain():

import itertools

l = ['a','b','c']

new_list = list(itertools.chain.from_iterable([[i, i+"_ind"] for i in l]))

print new_list

Output:

['a', 'a_ind', 'b', 'b_ind', 'c', 'c_ind']

It can be shortened a little bit by moving the options to the inner for loop in the list comprehension:

a = ['a','b','c']

[item for x in a for item in (x, x + '_ind')]
# ['a', 'a_ind', 'b', 'b_ind', 'c', 'c_ind']

You could make it a generator:

def mygen(lst):
    for item in lst:
        yield item
        yield item + '_ind'

>>> a = ['a','b','c']
>>> list(mygen(a))
['a', 'a_ind', 'b', 'b_ind', 'c', 'c_ind']

You could also do it with itertools.product, itertools.starmap or itertools.chain or nested comprehensions but in most cases I would prefer a simple to understand, custom generator-function.

---

With python3.3, you can also use yield from—generator delegation—to make this elegant solution just a bit more concise:

def mygen(lst):
    for item in lst:
        yield from (item, item + '_ind')

Another alternative with splicing (Python2.x, 3.x):

result = [None] * len(a) * 2
result[::2], result[1::2] = a, map(lambda x: x + '_ind', a)

result
# ['a', 'a_ind', 'b', 'b_ind', 'c', 'c_ind']