center (width, fillchar)

Returns a string with the original string centered to a total of width columns and filled with fillchar in columns that do not have characters

>>> strl="Welcome" >>> print(strl center(15,'*')) ****Welcome****

When the slicing operation, you can specify a third argument as the stride, which refers to the number of characters to move forward after the first character is retrieved from the string. The default value of stride is 1.

General format of slice operation:
str[start:end]
Where start is the beginning index and end is the last index value of a character in the string. Python takes the end value less than one from the actual index specified.

(i) Slice is a substring of a main string. A substring can be taken from the original string by using [ ]. operator and index or subscript values. 
(ii) Thus, [ ] is also known as slicing operator.Using slice operator, you have to slice one or more substrings from a main string.
General format of slice operation :
Str [start : end]

Strings in python are immutable. That means, once you define a string moditications or deletion is not allowed. However, we can replace the existing string entirely with the new string.

Membership Operators:
(i) The 'in' and 'not in' operators can be used with strings to determine whether a string is present in another string. Therefore, these operators are called as Membership Operators.
(ii) Example:
str1=input ("Enter a string:")
str2="chennai"
if str2 in str1:
print ("Found")
else:
print ("Not Found")
(iii) Output:1
Enter a string: Chennai GHSS, Saidapet
Found
(iv) Output:2
Enter a string: Govt GHSS, Ashok Nagar Not Found

(i) False
(ii) False
(iii) False

(i) 11
(ii) School
(iii) * * * * Welcome * * * *

str1 = input ("Enter a string:")
Index=-1
while index >= -(lentstrl1)):
print ("Subscript[",index,"] :" + str1 [index])
index +=-1
Output:
Enter a string: welcome
Subscript [ -1 ] : e
Subscript [ -2 ] : m
Subscript [ -3 ] : 0
Subscript [ -4 ] : c
Subscript [ -5 ] : I
Subscript [ -6 ] : e
Subscript [ -7 ] : w

Output:
Weool

str1=input ("Enter a string:")
str2="aAeEiloOuU"
v,c=0,0
for i in str1:
if i in str2:
v+=1
else:
c+=1
print ("The given string contains {} vowels and {} consonants".format(v.c))
Output:
Enter a string: Tamilnadu School Education.
The given string contains 11 vowels and 15 consonants.

str1 = input ("Enter a string:")
str2 ="
index=-1
for i in str1:
str2 += str1[index]
index -=1
print ("'The given string = {} \n The Reversed string = {}".format(str1, str2))
if (str1==str2):
print ("Hence, the given string is Palindrome")
else:
print ("Hence, the given is not a palindrome")
Output:1
Enter a string: malayalam
The given string = malayalam
The Reversed string = malayalam
Hence, the given string is Palindrome
Output: 2
Enter a string: welcome
The given string = welcome
The Reversed string = emoclew
Hence, the given string is not a palindrome