String Slicing

M3-R5.1 · Chapter 5: Sequence Data Types · 5 min read

String Slicing:  As we know slice means “part of”. So slicing is a process of extracting part of string

OR

Slicing in Python refers to extracting a portion (or "slice") of a sequence type—like a list, tuple, string, or range—using a specific syntax.

Syntax:

                   Str [start : stop : step]

  • If step value is positive, then we move in forward direction.
  • If step value is negative, then we move in backward direction.
  • Missing index before colon is considered as 0
  • Missing index after colon is considered as length of string
  • Slice operator with strings may have third index. Which is known as step. It is optional.

Example:

str="welcome"

for i in range (len(str)):

    print(i,":",str[i])

0 : w

1 : e

2 : l

3 : c

4 : o

5 : m

6 : e

>>> str=”welcome”

>>>str[2:6]

Output: lcom

>>> str=”welcome”

>>>str[1:6:2]

Output: ecm

>>> str=”welcome”

>>>str[1:5:2]

Output: ec

>>> str=”welcome”

>>>str[:4]

Output: welc

>>> str=”welcome”

>>>str[2:]

Output: lcome

>>> str=”welcome”

>>>str[1: :2]

Output: ecm

>>> str=”welcome”

>>>str[: :2]

Output: wloe

>>> str=”welcome”

>>>str[6]

Output: e

>>> str=”welcome”

>>>str[10]

Output: index out of range

>>> str=”welcome”

>>>str[10:  :]

Output: “ “

Example:

>>>text = "Prakash, Mishra"

>>>print(text[0:5])

                   Praka

>>>print(text[7:])

                 , Mishra

>>>print(text[:5])

                 Praka

>>> print(text[::2])

                Paah iha

Interesting Fact: Index out of bounds causes error with strings but slicing a string outside the index does not cause an error.

 >>>str[14]

IndexError: string index out of rang

>>> str[14:20] # both indices are outside the bounds

                          ' ' # returns empty string

Example:  Write a program to print the character with +ve and -ve Index number

str="welcome"

j=len(str)

for i in range (j):

    print(i,":",str[i],-j)

    j=j-1

0 : w -7

1 : e -6

2 : l -5

3 : c -4

4 : o -3

5 : m -2

6 : e -1

Example:

 

>>> str=”welcome”

>>>str[-6 :]

Output: elcome

>>> str=”welcome”

>>>str[-6 :-1:-2]

Output: “ “

>>> str=”welcome”

>>>str[-6 :-1:2]

Output: ecm

 

>>> str=”wonderful”

>>>str[0:6]

Output: wonder

>>> str=”wonderful”

>>>str[0:3]

Output: won

>>> str=”wonderful”

>>>str[3:6]

Output: der

>>> str=”wonderful”

>>>str[-1:-3]

Output: “”

>>> str=”wonderful”

>>>str[-3:-1]

Output: fu

>>> str=”wonderful”

>>>str[-3:0]

Output: “

>>> str=”wonderful”

>>>str[0: :2]

Output: wnefl

>>> str=”wonderful”

>>>str[3:3]

Output:  ‘ ‘

>>> str=”wonderful”

>>>str[3:4]

Output: d

>>> str=”wonderful”

>>>str[-5:-2]

Output: erf

>>> str=”wonderful”

>>>str[:-2]

Output: wonderf

>>> str=”wonderful”

>>>str[:4]

Output: wond

>>> str=”wonderful”

>>>str[-3]

Output: ful

>>> str=”wonderful”

>>>str[: : -1]

Output: lufrednow
                 

 

NOTE: For any index position n: str1[:n] +str1[n:] will give you the original string

Syntax:  str1[:n]+str1[n:]        #  output will be string  # where n is size of string

>>>str1=”welcome”

>>> str1[:7] + str1[7:]     

           Welcome

NOTE: String slicing will never return error even if you pass index which is not in the string.

Example:

>>> str1[10]           will give error, but

>>> str1[10:15]     will not give error but return empty string

Example:

Forward Indexing

S=”PYTHON PROGRAMMING”

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

P

Y

T

H

O

N

P

R

O

G

R

A

M

M

I

N

G

-18

-17

-16

-15

-14

-13

-12

-11

-10-

-9

-8

-7

-6

-5

-4

-3

-2

-1

            Backward Indexing

Example:

   >>> s[: :-2]

>>> s[2:3]

>>> s[2:3:-1]

>>> s[2:3:-1]

>>> s[2:3:-1]

>>> s[-6:7:-2]

Output:

GIMROPNHY

Output:  T

Output:  “  “

Output:  “  “

Output:  H

Output:  AGR

>>> S[9: -10]

>>> S[9: -10:-1]

>>> S[22: :-6]

>>> S[2:-22:-1]

>>> S[7:-1]

  >>> s[4:-8]

Output:“ “

Output:“O”

Output:“GRN”

Output:“TYP”

Output:“PROGRAMMING”

Output:

ON PRO