Return multiple values with generator expression

Question

I have a list

a = ["a", "b", "c"]

I want to create a new list with duplicate values with suffix("_ind").

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

I know it can be achieved using the following function(List with duplicated values and suffix)

def duplicate(lst):
    for i in lst:
      yield i
      yield i + "_ind"

How the same functionality can be achieved using generator expression?. I tried with the following code, But it is not working.

duplicate = (i i+'_ind' for i in a) 

File "<stdin>", line 1
duplicate = (i i+'_ind' for i in a)
            ^
SyntaxError: invalid syntax

Like the second answer in that question you linked to, except trivially turn the list comprehension into a generator. — Stefan Pochmann, Sep 24 '17 at 05:28

score 3 · Accepted Answer · answered Sep 24 '17 at 05:25

3

Use

duplicate = (j for i in a for j in (i, i+'_ind'))

answered Sep 24 '17 at 05:25

Oluwafemi Sule

36,144
1
56
81

score 1 · Answer 2 · answered Sep 24 '17 at 05:27

When yield are used in the function, they return a value of each yield statement. That means, if you have two yields, each yields will return a single value at each step. However, in the generator expression you can't return two values keeping the return value flat, instead you'll have to return it as tuple. But you can flatten the tuple at the time of extracting value. So, for you case, you may do:

>>> a = ["a", "b", "c"]
>>> duplicate = ((i, i+'_ind') for i in a)
#                 ^ return it as a tuple

>>> [i for s in duplicate for i in s]
['a', 'a_ind', 'b', 'b_ind', 'c', 'c_ind']

OR, you may use the generator expression as mentioned in Oluwafemi Sule's answer

Return multiple values with generator expression

2 Answers2