Here is a simple way to flatten 2D list in python.
l = [ [1,2], [3,4], [6,7], [8, 9,10] ] sum( l,  )
This will result in
[1, 2, 3, 4, 6, 7, 8, 9, 10]
Why is this even working?
sum(an_iterable_object) will simply use the operator
+ for the iterable object that was passed on to it. I can take in an optional parameter, i.e.,
The operations would be like this:
result = where_should_the_summation_start or 0 for i in an_iterable_object: result = result + i
Suppose we have a nested list
[ [1,2,3], [4,5] ], for each iteration, sum would simply concat the sublists together.
And, this is much faster than list comprehensions.
%%timeit sum( l,  ) # 309 ns ± 27.4 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
%%timeit [i for sublist in l for i in sublist] # 588 ns ± 33.2 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)