String in list merges large list

for example,
["[1meme 2meme 3]","[4pje 5pje 6],"[7pje 8pje 9],"[10pr 11pje 12]]
merge into one big list
[1pint 2pint 3Min 4Min 5Min 6, 7pint 8pens, 10pr 11]
suppose that the length of the list is 20000, how to merge more quickly
use the list derivation
[x for j in res_str for x in eval (j)]
speed up
[x for j in res_str for x in eval (j)]
is not the best way to do this, please tell us how to merge the list more quickly and use the list derivation style
[x for j in res_str for x in eval (j)]
.

is there any other way than the generator?

Mar.21,2021

from itertools import chain


l = ['[1,2,3]','[4,5,6]','[7,8,9]','[10,11,12]']
res = chain(*map(eval, l))
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