00012.PYTHON - STRING MANIPULATION SLIDES

STRING
MANIPULATION
VINOD KUMARVERMA, PGT(CS), KV OEF KANPUR &
SACHIN BHARDWAJ, PGT(CS), KV NO.1 TEZPUR
for more updates visit: www.python4csip.com

TRAVERSING STRING
• It means accessing the individual characters of string i.e. from first character to
last character.
• Every character in string is at different index position i.e. from 0 to size-1
• For loop can be used to traverse the string very easily
• For .e.g
name="lovely"
for ch in name:
print(ch,'-',end='')
The above code will print l-o-v-e-l-y-

PROGRAM TO READ STRING AND
PRINT IN REVERSE ORDER
string1 = input("Enter any string ")
print("The Reverse of ", string1 , " is :")
length=len(string1)
for ch in range(-1,(-length-1),-1):
print(string1[ch])
The above code will print
Enter any string: karan
n
a
r
a
k VINOD KUMARVERMA, PGT(CS), KV OEF KANPUR &

PROGRAM TO INPUT STRING AND
PRINT SHORT FORM
string=input("Enter any string ")
print(string[0],".",end='')
for ch in range(1,len(string)):
if string[ch]==' ':
print(string[ch+1],".",end='')

PROGRAM TO INPUT ANY STRING AND
COUNT HOW MANY VOWELS IN IT

STRING OPERATORS
Two basic operators + and * are allowed
+ is used for concatenation (joining)
* Is used for replication (repetition)

EXAMPLE
A=“Tom”
B=“Jerry”
C=A+” & ”+B
print(C)
Note: you cannot add number and string using +

EXAMPLE
Line=“ go”
print(Line*3, ” Govinda”)
Note: you cannot multiply string and string using *
Only number*number or string*number is allowed

MEMBERSHIP OPERATORS
•Membership operators (in and not in) are used to
check the presence of character(s) in any string.
Example Output
„a‟ in „python‟ False
„a‟ in „java‟ True
„per‟ in „operators‟ True
„men‟ in „membership‟ False
„Man‟ in „manipulation‟ False
„Pre‟ not in „presence‟ True

COMPARISON OPERATORS
• We can apply comparison operators (==, !=,>,<,>=,<=) on string.
Comparison will be character by character.
str1=„program‟
str2=„python‟
str3=„Python‟
Example Output
str1==str2 False
str1!=str2 True
str2==„python‟ True
str2>str3 True
str3<str1 True
Comparison of string
will be based on
ASCII code of the
characters
Characters Ordinal/
ASCII code
A-Z 65-90
a-z 97-122
0-9 48-57

DETERMINING ORDINAL / UNICODE OF
A SINGLE CHARACTER
Python allows us to find out the ordinal position single character
using ord() function.
>>>ord(‘A’) output will be 65
We can also find out the character based on the ordinal value
using chr() function
>>>chr(66) output will be ‘B’

STRING SLICING
As we know slice means „part of‟, so slicing is a process of
extracting part of string. In previous chapters we already
discussed that string characters have their unique index
position from 0 to length-1 and -1 to –length(backward)
0 1 2 3 4 5 6
W E L C O M E
-7 -6 -5 -4 -3 -2 -1
Forward indexing
message
Backward indexing

STRING SLICING
>>> str1="wonderful"
>>> str1[0:6]
'wonder'
>>> str1[0:3]
'won'
>>> str1[3:6]
'der'
>>> str1[-1:-3]
''
>>> str1[-3:-1]
'fu'
>>> str1[-3:0]
'‘
>>>str1[0::2]
‘Wnefl’
>>> str1[3:3]
''
>>> str1[3:4]
'd'
>>> str1[-5:-2]
'erf'
>>> str1[:-2]
'wonderf'
>>> str1[:4]
'wond‘
>>> str1[-3:]
'ful‘
>>>str1[::-1]
lufrednow
Reverse
of string

INTERESTING STRING SLICING
For any index position n: str1[:n]+str1[n:] will give you the
original string
>>>str1=“wonderful”
>>>str1[:n]+str[n:] output will be wonderful
String slicing will never return error even if you pass index
which is not in the string . For e.g.
>>>str1[10] will give error, but
>>>str1[10:15] will not give error but return empty
string

PROGRAMS
Program to print the pattern
@
@@
@@@
@@@@
@@@@@
string='#'
pattern=''
for i in range(5):
pattern+=string
print(pattern)
Program to input name and print
as (if name is ‘AAMIR’), output
A
AA
AAM
AAMI
AAMIR
name=input("Enter any name")
for i in range(0,len(name)+1):
print(name[0:i])

STRING FUNCTIONS AND METHODS
Python offers many built-in function for string manipulation. One
method len() we have already used. Let us understand other
methods also.
To use string manipulation function the syntax is:
String_Object.functionName()

STRING FUNCTIONS/METHODS
• len(string) : this function returns the number of characters in any string
including spaces.
• capitalize() : this function is used to convert the first letter of sentence in
capital letter.
• title() : this function is used to convert first letter of every word in string in
capital letters.
• upper() : this function is used to convert the entire string in capital letter.

• lower() : this function is used to convert the entire string in small letter.
• count(substring, [start,[end]]) : this function is used to find the number of
occurrence of substring in our string. We can give optional starting index from
where searching begin and also end index i.e. upto what index in string it will
search and count. It return 0 if substring not found.
• find(substring,[start,[end]]) : this function returns the index position of
substring in the given string. We can also specify start and end index just like
count() to modify search criteria. It return -1 if substring not found/

• index(substring) : this function return index position of substring. If
substring not it returns error ‘substring not found’
• isalnum() : this function is used to check where string contain all character
as alphanumeric or not. Its return is either True or False.
• islower(): this function return True if all the characters in string is in small
letters
• isupper() : this function return True if all the characters in string is in capital
letters. Both islower() and isupper() will check the case only for letter, if any
symbol present in string it will be ignored.

• isspace() :.it return True if the string contains only space.
• isalpha() : it return True if all the characters in string is alphabet.
• isdigit() : it returns True if all the characters in string is digit.

• split() : this function is used to split the string based on delimiter and store
the result in the form of list. Default delimiter is space.
• partition(sep) : this function divides the string in the form of tuples of 3
elements known as head, sep and tail. All the string before sep becomes
head and all the string after sep becomes tail. If sep is not present in the
string then everything will becomes head, sep and tail will be empty.

• strip([chars]) : it return a copy of string with leading and trailing whitespaces
removed. If chars is given, it remove characters instead.
• lstrip([chars]) : it return a copy of string with leading whitespaces removed. If
chars is given, it remove characters instead.
• rstrip([chars]) : it return a copy of string with trailing whitespaces removed. If
chars is given, it remove characters instead.
• Note: if chars is given in any strip() function, the chars are checked for all the
possible combination that can be formed with the given chars. For e.g. if NOT
is passed as char then NOT, OTN, TON, TNO, ONT,NT like this every possible
combination will be checked.

STRING FUNCTION / METHODS
• replace(old, new) : this function is used to replace old text inside the string
with new text.

PROGRAM TO ENTER STRING AND COUNT HOW MANY
UPPERCASE, LOWERCASE, DIGITS, WORDS PRESENT IN IT.

PROGRAM TO ENTER STRING AND FIND THE NUMBER OF
OCCURANCE OF ANY WORD

JUST A MINUTE…
Find out output of following code fragment:
s1='try'
s2='again'
n1=8
n2=5
print(s1+s2)
print(s2*n2)
print(s1+n1)
print(s2*s1)

CONSIDER THE FOLLOWING CODE: WHAT WILL BE THE
OUTPUT IF INPUT IS
string = input("Enter a string :")
count=3
whileTrue:
if string[0]=='a':
string = string[2:]
elif string[-1] == 'b':
string=string[:2]
else:
count+=1
break
print(string)
print(count)
(i) aabbcc (ii) aaccbb (iii) abcc

CONSIDER THE FOLLOWING CODE: WHAT WILL BE THE
OUTPUT IF INPUT IS
string = input("Enter a string :")
count=3
whileTrue:
if string[0]=='a':
string = string[2:]
elif string[-1] == 'b':
string=string[:2]
else:
count+=1
break
print(string)
print(count)
(i) aabbcc (ii) aaccbb (iii) abcc
If input is aabbcc, output will be
bbcc
4
If input is aaccbb, output will be
cc
4
If input is abcc, output will be
cc
4

WHAT WOULD FOLLOWING EXPRESSION RETURN?
a) “HelloWorld”.upper().lower()
b) “HelloWorld”.lower().upper()
c) “HelloWorld”.find(“Wor”,1,6)
d) “HelloWorld”.find(„Wor‟)
e) “HelloWorld”.find(„wor‟)
f) “HelloWorld”.isalpha()
g) “HelloWorld”.isalnum()
h) “1234”.isdigit()
i) “123GH”.isdigit()

OUTPUT?
(a)
s="0123456789"
print(s[3],',',s[0:3],'-',s[2:5])
print(s[:3],',',s[3:],'-',s[3:100])
print(s[20:],',',s[2:1],'-',s[1:1])
(b)
y=str(123)
x="hello"*3
print(x,y)
x = "hello" + "world"
y=len(x)
print(y,x)

00012.PYTHON - STRING MANIPULATION SLIDES

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