join method for string

The line return ''.join(x) is a Python expression 
used to convert a list of characters back into a single string.


'' (Empty String):

    The '' is the string that you want to use as 
a separator between the elements of the list. 
In this case, it's an empty string, 
so no additional characters will be added between the elements when joining them.

.join(iterable):

    The .join() method is a string method in Python.
It takes an iterable (such as a list, tuple, or any sequence of strings) 
as an argument and combines all the elements of that iterable into a single string.
    Each element of the iterable must be a string.

The List x:

    In your code, x is a list of characters (because list(x) was 
used to convert the input string into a list). For example:




How It Works:

    The join method combines all the characters (
or strings) in the list x into a single string. 
Since the separator is an empty string '', it simply concatenates
them together without adding anything in between.




x = ['H', 'e', '*', '*', 'o']




result:

    After joining, the list ['H', 'e', '*', '*', 'o'] becomes the string "He**o".