Python String join() Method

join() is an inbuilt string function in Python used to join elements of the sequence separated by a string separator. This function joins elements of a sequence and makes it a string. 

Syntax: string_name.join(iterable) 

Parameters:

• Iterable – objects capable of returning their members one at a time. Some examples are List, Tuple, String, Dictionary, and Set

Return Value: The join() method returns a string concatenated with the elements of iterable. 

Type Error: If the iterable contains any non-string values, it raises a TypeError exception. 

Example 1: Joining with an empty string

Here, we join the list of elements using the join method.

Python3

# Joining with empty separator
list1 = ['g', 'e', 'e', 'k', 's']
print("".join(list1))

# Joining with string
list1 = " geeks "
print("$".join(list1))

Output: 

geeks
$g$e$e$k$s$ 

Time Complexity: O(n)
Auxiliary Space: O(n)

Example 2: Joining String with lists using join()

Here, we join the tuples of elements using the join() method in which we can put any character to join with a string.

Python3

# elements in tuples
list1 = ('1', '2', '3', '4')

# put any character to join
s = "-"

# joins elements of list1 by '-'
# and stores in string s
s = s.join(list1)

# join use to join a list of
# strings to a separator s
print(s)

Output: 

1-2-3-4

Time Complexity: O(n)
Auxiliary Space: O(n)

Example 3: Joining String with sets using join()

In this example, we are using a Python set to join the string.

Note: Set contains only unique value therefore out of two 4 one 4 is printed.

Python3

list1 = {'1', '2', '3', '4', '4'}

# put any character to join
s = "-#-"

# joins elements of list1 by '-#-'
# and stores in string s
s = s.join(list1)

# join use to join a list of
# strings to a separator s
print(s)

Output: 

1-#-3-#-2-#-4

Time Complexity: O(n)
Auxiliary Space: O(n)

Example 4: Joining String with a dictionary using join()

When joining a string with a dictionary, it will join with the keys of a Python dictionary, not with values.

Python3

dic = {'Geek': 1, 'For': 2, 'Geeks': 3}

# Joining special character with dictionary
string = '_'.join(dic)

print(string)

Time Complexity: O(n)
Auxiliary Space: O(n)

Output:

'Geek_For_Geeks'