Python | Ways to concatenate two lists 连接两个list

Method #1: Using + operator

The most conventional method to perform the list concatenation, the use of “+” operator can easily add the whole of one list behind the other list and hence perform the concatenation.

# Python 3 code to demonstrate list 
# concatenation using + operator 

# Initializing lists 
test_list3 = [1, 4, 5, 6, 5] 
test_list4 = [3, 5, 7, 2, 5] 

# using + operator to concat 
test_list3 = test_list3 + test_list4 

# Printing concatenated list 
print ("Concatenated list using + : "
				+ str(test_list3)) 

Method #2 : Using list comprehension

List comprehension can also accomplish this task of list concatenation. In this case, a new list is created, but this method is a one liner alternative to the loop method discussed above.

# Python3 code to demonstrate list 
# concatenation using list comprehension 

# Initializing lists 
test_list1 = [1, 4, 5, 6, 5] 
test_list2 = [3, 5, 7, 2, 5] 

# using list comprehension to concat 
res_list = [y for x in [test_list1, test_list2] for y in x] 

# Printing concatenated list 
print ("Concatenated list using list comprehension: "
									+ str(res_list)) 

Method #3 : Using extend()

extend() is the function extended by lists in Python and hence can be used to perform this task. This function performs the inplace extension of first list.

# Python3 code to demonstrate list 
# concatenation using list.extend() 

# Initializing lists 
test_list3 = [1, 4, 5, 6, 5] 
test_list4 = [3, 5, 7, 2, 5] 

# using list.extend() to concat 
test_list3.extend(test_list4) 

# Printing concatenated list 
print ("Concatenated list using list.extend() : "
							+ str(test_list3)) 

Method #4 : Using * operator

Using * operator, this method is the new addition to list concatenation and works only in Python 3.6+. Any no. of lists can be concatenated and returned in a new list using this operator.

# Python3 code to demonstrate list 
# concatenation using * operator 

# Initializing lists 
test_list1 = [1, 4, 5, 6, 5] 
test_list2 = [3, 5, 7, 2, 5] 

# using * operator to concat 
res_list = [*test_list1, *test_list2] 

# Printing concatenated list 
print ("Concatenated list using * operator : "
							+ str(res_list)) 

Method #5 : Using itertools.chain()

itertools.chain() returns the iterable after chaining its arguments in one and hence does not require to store the concatenated list if only its initial iteration is required. This is useful when concatenated list has to be used just once.

# Python3 code to demonstrate list 
# concatenation using itertools.chain() 
import itertools 

# Initializing lists 
test_list1 = [1, 4, 5, 6, 5] 
test_list2 = [3, 5, 7, 2, 5] 

# using itertools.chain() to concat 
res_list = list(itertools.chain(test_list1, test_list2)) 

# Printing concatenated list 
print ("Concatenated list using itertools.chain() : "
									+ str(res_list))