What is the fastest way to merge two lists in python?

Question

Given,

list_1 = [1,2,3,4]
list_2 = [5,6,7,8]

What is the fastest way to achieve the following in python?

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Answer 1

I tested out several ways to merge two lists (see below) and came up with the following order after running each several times to normalize the cache changes (which make about a 15% difference).

import time
c = list(range(1,10000000))
c_n = list(range(10000000, 20000000))
start = time.time()
*insert method here* 
print (time.time()-start)

• Method 1: c.extend(c_n)

  • Representative result: 0.11861872673034668

• Method 2: c += c_n

  • Representative result: 0.10558319091796875

• Method 3: c = c + c_n

  • Representative result: 0.25804924964904785

• Method 4: c = [*c, *c_n]

  • Representative result: 0.22019600868225098

Conclusion Use += or .extend() if you want to merge in place. They are significantly faster.