Python Join List

In this topic, we will discuss how we can join two or more lists with different functions of Python. Before going through the concepts, let's take a brief introduction to the Python List. A Python List is the collection of multiples items that are grouped in the same name. It can store different data types (integer, string, float, etc.) items inside a square bracket [], which is separated by a (,) comma.

Program to print the Python list

List.py

# list of characters
List1 = ['A', 'B', 'C', 'D', 'E']

# list of integers
List2 = [1, 2, 3, 4, 5,]

# mixed lists
List3 = ['A', 1, 'C', 'E', 5, 8]

print (" Display the List1 ", List1)
print (" Display the List2 ", List2)
print (" Display the List3 ", List3)

Output

Display the List1  ['A', 'B', 'C', 'D', 'E']
 Display the List2  [1, 2, 3, 4, 5]
 Display the List3  ['A', 1, 'C', 'E', 5, 8]

When we join two or more lists together in a Python program, it gives a joined lists. And this process is called composition or joining of lists.

Let's discuss the different ways to join two or more lists in Python:

Join lists in Python using the join() function and delimiters
Join a list in Python using the join() function without delimiters
Join two integers list in Python using map() function
Join two lists in Python using for loop and append() function
Join multiple lists in Python using itertools.chain() method
Join two lists in Python using (+) plus operator
Join two lists in Python using (*) multiply or asterisk operator
Join two lists in Python using extend() function

Join lists in Python using the join() function

A join() function is used to join an iterable list to another list, separated by specified delimiters such as comma, symbols, a hyphen, etc.

Syntax

str_name: It is the name of the delimiter that separates an iterable list.

iterable: It is the list that contains a set of elements and joins with a delimiter.

Return Value: It returns a concatenated list that is separated by specified delimiters.

Note: If the iterable list contains any non-string values or items, it throws a TypeError exception.

Program to join two lists using the join() function and delimiter

Join.py

List1 = [ "Apple", "Orange", "Banana", "Mango", "Grapes" ]
Str2 = ", " # It is the comma delimiter
# use join() function to join List1 with the " . " delimiter 
Str2 = Str2.join( List1)

# print the join list 
print (" Display the concatenated List1 using join() function and delimiter", Str2)

List2 = [  "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday" ]
Str3 = " - " # It is the hyphen delimiter
# use join() function to join List2 with the " - " delimiters 
Str3 = Str3.join( List2)

# print the join list 
print (" Display the concatenated List2 using join() function and delimiter", Str3)

Output

Display the concatenated List1 using join() function and delimiter Apple, Orange, Banana, Mango, Grapes
 Display the concatenated List2 using join() function and delimiter Sunday - Monday - Tuesday - Wednesday - Thursday

Program to join a list without using delimiter

Prog.py

# declare a python list 
Lt1 = [ 'j', 'a', 'v', 'a', 't', 'p', 'o', 'i', 'n', 't' ]
print ( " Display the elements of the List L1 " , Lt1)
L2 = '  '  # declare any empty string without defining any delimiter
Ret = L2.join( Lt1) # use join method to join L1 list with L2
print ( " Display the List without using delimiters", Ret)  

Output

Display the elements of the List L1  ['j', 'a', 'v', 'a', 't', 'p', 'o', 'i', 'n', 't']
 Display the List without using delimiters j  a  v  a  t  p  o  i  n  t

Join two integers list using map() function

Integer list: It collects all integers in a list called the integer list, and we cannot join two integer lists in Python using the join() function. Therefore, we use a map() function that converts an integer list into a string. After that, we use a join() function to join map() function results with appropriate delimiters.

Syntax:

In the above syntax, a map() function has two parameters, list_name, and str. Where list_name is the name of integers list and str represents the string. A map() function converts the list_name into the string (str).

Program to use a map() function and join() function in list

Let's create a program to convert the given integers list into a string using the map() function and then join() function to join the list.

Convert.py

lt = [1, 2, 3, 4, 5]
# use map() function to convert integer list into string 
list_map = map(str, lt)
lt2 = ', '

# use join() function to join lists and delimiter comma (,) 
res = lt2.join (list_map)
print (" Display the concatenated integers list using map() and join() function ", res)

Output

Display the concatenated integers list using map() and join() function  1, 2, 3, 4, 5

Program to join two lists in Python using for loop and append() function

An append() function is used to sequentially add or join each element of an iterable list at the end of another list using for loop. Let's create a simple program to add elements of a list at the end of another list using the append() function.

Append.py

List1 = [1, 2, 3, 4, 5] # declare List1
List2 = [5, 6, 7, 8, 9, 10] # declare List2

print (" Given List1 ", List1)	
print (" Given List2 ", List2)

# use for loop to iterate each element of Lt1 to l2
for i in List2:
    List1.append(i) # use append() function to insert each elements at the end of Lt1
print (" Display concatenation list using append() function ", List1)    

Output

Given List1  [1, 2, 3, 4, 5]
 Given List2  [5, 6, 7, 8, 9, 10]
 Display concatenation list using append() function  [1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 10]

Program to join multiple lists using itertools.chain() method

Let's create a simple program in Python to concatenate multiple lists using the chain() method by importing the itertools package.

New.py

# use Python itertools.chain() method to join two list
import itertools

# declare different lists
a = [1, 2, 3, 4, 5]
b = [6, 7, 8, 9, 10]
c = [11, 12, 13, 14, 15]
print (" Display the first list ", a)
print (" Display the second list ", b)
print (" Display the third list ", c)

# use itertools.chain() method to join the list
result = list (itertools.chain (a, b, c))

# pass the result variable in str() function to return the concatenated lists
print (" Concatenated list in python using itertools.chain() method ", str (result))

Output

Display the first list  [1, 2, 3, 4, 5]
 Display the second list  [6, 7, 8, 9, 10]
 Display the third list  [11, 12, 13, 14, 15]
 Concatenated list in python using itertools.chain() method  [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]

Program to join two lists using + operator

Let's consider an example to join two lists in Python using the (+) plus operator.

Mypro.py

# Create a program to join two lists in Python using the '+' operator
	
# declare two lists of characters
list1 = [ 'A', 'B', 'C', 'D', 'E']
list2 = [ 'F', 'G', 'H', 'I', 'J']

# join two characters lists using '+' operator
lt_sum1 = list1 + list2


# declares two lists of integers
list3 = [ '1', '2', '3', '4', '5']
list4 = [ '6', '7', '8', '9', '10']

# join two integers lists using '+' operator
lt_sum2 = list3 + list4

# display the concatenation list
print (" Join two list of characters in Python using + operator: ", str(lt_sum1))

# display the concatenation list
print (" Join two list of integers in Python using + operator: ", str(lt_sum2))

Output

Join two list of characters in Python using + operator:  ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J']
 Join two list of integers in Python using + operator:  ['1', '2', '3', '4', '5', '6', '7', '8', '9', '10']

Program to join two list using (*) multiply operator

Consider an example to join two lists of in Python using * operator.

Mypro2.py

# declare two lists of characters
List1 = [ 'A', 'B', 'C', 'D', 'E']
List2 = [ 'F', 'G', 'H', 'I', 'J']
print (" Display character List1 ", List1)
print (" Display character List2 ", List2)

# join two characters lists using '*' operator
lt_sum1 = [*List1, *List2]


# declares two lists of integers
List3 = [ 1, 2, 3, 4, 5]
List4 = [ 6, 7, 8, 9, 10]
print (" Display integer List3 ", List3)
print (" Display integer List4 ", List4)
# join two integers lists using '*' operator
lt_sum2 = [*List3, *List4]

# display the concatenation list
print (" Join two characters list in Python using * operator: "+ str(lt_sum1))

# display the concatenation list
print (" Join two integers list in Python using * operator: "+ str(lt_sum2))

Output

Display integer List3  [1, 2, 3, 4, 5]
 Display integer List4  [6, 7, 8, 9, 10]
 Join two characters list in Python using * operator: ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J']
 Join two integers list in Python using * operator: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Program to join two lists in Python using extend() method

Let's write a simple program to join two lists using extend() method in Python.

Prog.py

# takes two integers lists
List1 = [5, 10, 5]
List2 = [ 2, 4, 6, 8]
print (" Display the List1 ", List1)
print (" Display the List1 ", List2)

# takes two string lists
List3 = [ 'RED', 'BLUE', 'BLACK']
List4 = [ 'BROWN', 'PURPLE', 'GREY' ]
print (" Display the List3 ", List3)
print (" Display the List4 ", List4)


# use extend() method to join two lists
List1.extend(List2)
List3.extend(List4) 

# print concatenation lists
print( "\n Adding two lists of integers in Python using the extend() function: ", str(List1))
print( "\n Adding two lists of strings in Python using the extend() function: ", str(List3))

Output

Display the List1  [5, 10, 5]
 Display the List1  [2, 4, 6, 8]
 Display the List3  ['RED', 'BLUE', 'BLACK']
 Display the List4  ['BROWN', 'PURPLE', 'GREY']

 Adding two lists of integers in Python using the extend() function:  [5, 10, 5, 2, 4, 6, 8]

 Adding two lists of strings in Python using the extend() function:  ['RED', 'BLUE', 'BLACK', 'BROWN', 'PURPLE', 'GREY']

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