String in Python
§ Strings are sequences of
characters.
§ Python has a built-in string
class named "str" with many handy features.
§ String literals can be
enclosed by either double or single quotes.
§ Python strings are
"immutable" which means they cannot be changed after they are
created.
How to create a string and assign it to a variable
§ To create a string, put the
sequence of characters inside either single quotes, double quotes, or triple
quotes and then assign it to a variable
§ Even triple quotes can be
used in Python but generally used to represent multiline strings and
docstrings.
# all of the following
are equivalent
my_string = 'Hello'
print(my_string)
my_string = "Hello"
print(my_string)
my_string = '''Hello'''
print(my_string)
# triple quotes string
can extend multiple lines
my_string = """Hello,
welcome to
the world of Python"""
Hello
Hello
Hello
Hello, welcome to
the world of Python
How to access Character from the string:
§ There are two ways to access character from the
string.
1.
By using Index
2.
By using slice
operator
1. By using index
§ Characters in a string can be accessed using the standard [ ]
§ In python string having both +ve and -ve index. i.e.
we can access character from string using +ve and -ve index.
§ +ve index means going to forward direction (Left to
Right)
§ -ve index means going to backward direction (Right to
Left)
s="python"
print(s[0]) #output
will be p
print(s[-6]) #output
will be p
print(s[-1]) #output will be n
Take
an input from the user and display each character and its index position.
s=input('enter string')
i=0
for x in s:
print('The character {} present at positive index {}'.format(x,i))
print('The character {} present at Negative index {}'.format(x,i-len(s)))
i=i+1
#The Output will be
enter string
python
The character p present at positive index 0
The character p present at Negative index -6
The character y present at positive index 1
The character y present at Negative index -5
The character t present at positive index 2
The character t present at Negative index -4
The character h present at positive index 3
The character h present at Negative index -3
The character o present at positive index 4
The character o present at Negative index -2
The character n present at positive index 5
The character n present at Negative index -1
By Using Slice
Operator:
s[beginindex:endindex:step]
§ from begin index to end-1 index and every
time update by step
§ default value for begin index is zero.
§ default value for end index is length of
string.
s[begin:end:step]
§ step value can be either +ve or -ve.
§ if +ve then it should be forward direction
(Left to Right).
§ If -ve then it should be backward
direction (Right to Left).
§ If +ve forward direction from begin to
end-1.
§ if -ve backward direction from begin to
end+1
s='python'
print(s[0:5]) # the output will be pytho
print(s[0:6]) # the output will be python
print(s[0:70]) # the output will be python
print(s[6:10]) # the output will be blank string becoz there is no
specified
substring
in given range
print(s[0:6:2]) # the output will be pto
print(s[5:0:-1]) # the output will be nohty
print(s[2:8:-1]) # the output will be blank
string
print(s[-1:-7:-1]) # the output will be nohtyp
v If you omit the first index, the slice starts at the
beginning of the string. Thus, s[:m] and s[0:m] are equivalent:
s[:endindex]
s='python'
print(s[:4])#The Output Will be pyth
print(s[0:4])#The Output Will be pyth
v if you omit the second index as in s[n:], the slice
extends from the first index through the end of the string. This is a nice,
concise alternative to the more cumbersome s[n:len(s)]:
s[beginindex:]
s='python'
print(s[2:])#The Output Will be thon
print(s[2:len(s)])#The Output Will be thon
v If
you Omitting both indices return the original string.
s[:]
s='python'
print(s[:])#The
Output Will be python
print(s[0: len(s)])#The Output Will be python
v If
the first index in a slice is greater than or equal to the second index, Python
returns an empty string.
s='python'
print(s[2:2])#The
Output Will be empty string
print(s[4:2])#The Output Will be empty string
In forward Direction
§ default value for begin: 0
§ default value for end: length of the
string
§ default value for step: 1
In backward direction
§ default value for begin index: -1
§ default value for end: -(length of
string+1)
s='python'
print(s[-1::-1]) #the output
will be nohtyp
# default value for end index is
(len(s)+1)
# end:- -(6+1)=-7
# In Backward direction
# begin to end+1
# -1 to -7+1
# -1 to -6
Reversing a string
s=input('enter
string')
rev=s[::-1]
print('Original
String: ',s)
print('Reverse String: ',rev)
Output:
enter string hello
Original String: hello
Reverse String: olleh
Check
Given String is a Palindrome or Not?
def isPalindrome(s):
rev=s[::-1]
if
s==rev:
return True
else:
return False
s=input('enter
string')
result=isPalindrome(s)
if
result==True:
print(s,' is
a Palindrome String')
else:
print(s,' is
not a Palindrome String')
Output:
enter stringmadam
madam is a Palindrome String
Iterating
Through String
§ Using
for loop we can iterate through a string.
for letter in 'Hello':
print(letter)
Output
H
e
l
l
o
Write a python
program for finding how many times any character occur in given string
s=input('enter
string')
ch=input('enter
letter for found')
count=0
for
letter in s:
if
letter==ch:
count+=1
print(count,'times',ch,' letters found in',s)
Output
enter stringhello
enter letter for foundl
2 times l letters found
in hello
String Operators In
Python
The +
Operator
§ The
+ operator concatenates strings.
§ If
we want to use + operator for str type then compulsory both arguments should be
str type only otherwise we will get error.
a='hello'
b='world'
c='python'
d=10
print(a+b)#The Output Will be helloworld
print(a+b+c)#The Output Will be helloworldpython
print(a+d)
TypeError: can only concatenate str (not "int") to str
The *
Operator
§ The
* operator creates multiple copies of a string.
§ If
we use * operator for str type then compulsory one argument should be int and
other argument should be str type.
s='hello'
print(s*5)
#The Output Will be
hellohellohellohellohello
The in Operator
Checking
Membership(String Contains):
§ We
can check whether a string contains a given substring or not. Just use the in operator:
str='python is a prog lang'
print('python' in str)#the
output will be True
Note:
testing an empty string will always result in True:
print("" in "test")#the
output will be True
s='python'
print('p'in s) # The OutPut Will be True
print('po' in s) #
The OutPut Will be False
print('py' in s) #
The OutPut Will be True
print('po' not in s) #
The OutPut Will be True
Write a python
program for check sub string exists within a string or not
main=input('enter main string')
subs=input('enter sub string to serach')
if subs in main:
print(subs,"is found in",main)
else:
print(subs,"sub
string is not found in",main)
Write a python
program for removal of vowels in given string
s=input('enter
string')
vows=''
for ch in s:
if ch in'aeiou':
vows+=ch
print('Original
String:- ',s)
print('After Removel of Consonaunt:-
',vows)
Output
enter stringhello
Original String:- hello
After Removel of
Consonaunt:- eo
Write a python
program for removal of consonant in given string
s=input('enter string')
cons=''
for ch in s:
if ch not in'aeiou':
cons+=ch
print('Original
String:- ',s)
print('After Removel of
Vowel:- ',cons)
Output
enter stringhello
Original String:- hello
After Removel of
Vowel:- hll
Important
Points:
§ Python
provides many functions that are built-in to the interpreter and always
available. Here are a few that work with strings:
Function
|
Description
|
chr()
|
Converts
an integer to a character
|
ord()
|
Converts
a character to an integer
|
len()
|
Returns
the length of a string
|
str()
|
Returns
a string representation of an object
|
chr(n)
§ Returns
a character value for the given integer.
print(chr(65))# The
output Will be A
print(chr(97))# The
output Will be a
print(chr(57))# The output Will be 9
ord(c)
§ Returns
an integer value for the given character.
print(ord('a'))# The
output Will be 97
print(ord('A'))# The
output Will be 65
print(ord('#'))# The output Will be 35
len(s)
§ Returns
the length of a string.
s='hello world'
print(len(s))#The Output will be 11
str(obj)
§ Returns
a string representation of an object.
print(str(10))#The
Output will be '10'
print(str(2.3))#The
Output will be '2.3'
print(str((3+4j)))#The Output will be '(3+4j)'
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