Slicing ([:]) is an operation that can be performed on lists to retrieve a specific successive portion of the original list. Since strings are also lists of characters, slicing can be applied on the strings as well.

course = " Introduction to Programming"

print(course[1:13])

This first character in a string resides at index 0 and the [1:13] slice corresponds to the sub-string of the given string starting at index 1 and ending at index 12, excluding the given end index value 13, yielding the substring "Introduction". If no start index is specified for the slice, then it is assumed to be 0, i.e. the beginning index of the string. Similarly if no end-index is specified for the slice, it is assumed to be the length of the string.

course = "Introduction to Programming"

print(course[:12])

generates the output "Introduction", and similarly,

course = "Introduction to Programming"

print(course[16:])

produces the output "Programming".

The index values used in slicing can be bound to variables:

social_security_id = "25495-456-3224874"

for i in range(5,len(social_security_id)):
    print(i*"*" + social_security_id[i:len(social_security_id)])

The code above can be used to hide a certain part of the social security id numbers:

*****-456-3224874
******456-3224874
*******56-3224874
********6-3224874
*********-3224874
**********3224874
***********224874
************24874
*************4874
**************874
***************74
****************4

Try hiding the end or middle portion of the id number such as :

25495-456-322487*
25495-456-32248**
25495-456-3224***
25495-456-322****
25495-456-32*****

or 

25495-45*-3224874
25495-4***3224874
25495-*****224874
25495*******24874
2549*********4874

and maybe

*5495-456-322487*
**495-456-32248**
***95-456-3224***
****5-456-322****
*****-456-32*****
******456-3******