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In Built Function

len() Function

  • We can use len() function to find the number of characters present in the string.

Example

Python
s='ajay'
print(len(s))

Output

PowerShell
4

Question

Write a program to access each character of string in forward and backward direction by using while loop?

Python
s="Learning Python is very easy !!!"
n=len(s)
i=0
print("Forward direction")
while i<n:
    print(s[i],end=' ')
    i+=1
print()
print("Backward direction")
i=-1
while i>=-n:
    print(s[i],end=' ')
    i-=1

Output

PowerShell
Forward direction
L e a r n i n g   P y t h o n   i s   v e r y   e a s y   ! ! ! 
Backward direction
! ! !   y s a e   y r e v   s i   n o h t y P   g n i n r a e L
Alternative ways
Python
s="Learning Python is very easy !!!"
print("Forward direction")
for i in s:
    print(i,end=' ')
print()
print("Backward direction")
for i in s[::-1]:
    print(i,end=' ')

Output

PowerShell
Forward direction
L e a r n i n g   P y t h o n   i s   v e r y   e a s y   ! ! ! 
Backward direction
! ! !   y s a e   y r e v   s i   n o h t y P   g n i n r a e L

Removing Spaces

  • We can use the following 3 methods
    • rstrip() ⇒ To remove spaces at right hand side.
    • lstrip() ⇒ To remove spaces at left hand side.
    • strip() ⇒ To remove spaces both sides.

Example

Python
city=input("Enter your city Name:")
city=city.strip()
print("City name -", city)
if city=='Hyderabad':
    print("Hello Hyderbadi..Adab")
elif city=='Chennai':
    print("Hello Madrasi...Vanakkam")
elif city=="Bangalore":
    print("Hello Kannadiga...Shubhodaya")
else:
    print("your entered city is invalid")

Output

PowerShell
Enter your city Name:   Allahabad   
City name - Allahabad
your entered city is invalid
PowerShell
Enter your city Name:Chennai
City name - Chennai
Hello Madrasi...Vanakkam

Finding Substrings

  • We can use the following 4 methods
    • For forward direction
      • find()
      • index()
    • For backward direction
      • rfind()
      • rindex()

find()

Syntax

Python
main_string.find(sub_string, begin_index, end_index)
  • Return index of first occurrence of the given substring between begin_index and end_index. If it is not available then we will get -1.
  • default value of begin_index = 1 and end_index = length of string.

Example

Python
s="Learning Python is very easy"
print(s.find("Python"))
print(s.find("Java"))
print(s.find("r"))
print(s.rfind("r"))

Output

Python
9
-1
3
21

Example

Python
s="Learning Python is very easy"
print(s.find("Python", 7, 15))
print(s.find("Java, 7, 15"))
print(s.find("o", 7, 15))
print(s.rfind("r", 7, 15))

Output

Python
9
-1
13
-1

index()

  • index() method is exactly same as find() method except that if the specified substring is not available then we will get ValueError.

Example

Python
s=input("Enter main string:")
subs=input("Enter sub string:")
try:
    n=s.index(subs)
except ValueError:
    print("substring not found")
else:
    print("substring found")

Output

PowerShell
Enter main string:learning python is very easy
Enter sub string:python
substring found
PowerShell
Enter main string:learning python is very easy
Enter sub string:java
substring not found

Question

Display all positions of substring in a given main string

Python
s=input("Enter main string:")
subs=input("Enter sub string:")
flag=False
pos=-1
n=len(s)
while True:
    pos=s.find(subs,pos+1,n)
    if pos==-1:
        break
    print("Found at position",pos)
    flag=True
if flag==False:
    print("Not Found")

Output

PowerShell
Enter main string:ajay shukla
Enter sub string:a
Found at position 0
Found at position 2
Found at position 10

Counting Substring

  • We can find the number of occurrences of substring present in the given string by using count() method.
    • s.count(substring) ⇒ It will search through out the string.
    • s.count(substring, begin_index, end_index) ⇒ It will search from begin_index to end_index-1.

Example

Python
s="abcabcabcabcadda"
print(s.count('a'))
print(s.count('ab'))
print(s.count('a',3,7))

Output

PowerShell
6
4
2

Replacing Substring

  • s.replace(old_string, new_string)
    • Inside s, every occurrence of old_string will be replaced with new_string.

Example

Python
s="Learning Python is very difficult"
s1=s.replace("difficult","easy")
print(s1)

Output

PowerShell
Learning Python is very easy

Example

Python
s="ababababababab"
s1=s.replace("a","b")
print(s1)

Output

PowerShell
bbbbbbbbbbbbbb

Question

String objects are immutable then how we can change the content by using replace() method.

Answer

  • Once we creates string object, we cannot change the content. This non changeable behavior’s is nothing but immutability. If we are trying to change the content by using any method, then with those changes a new object will be created and changes won’t be happened in existing object.
  • Hence with replace() method also a new object got created but existing object won’t be changed.
Python
s="abab"
s1=s.replace("a","b")
print(s,"is available at :",id(s))
print(s1,"is available at :",id(s1))

Output

Python
abab is available at : 2711833054000
bbbb is available at : 2711839144688

Splitting of Strings

  • We can split the given string according to specified separator by using split() method.
    • s.split(separator)
    • The default separator is space.
    • The return type of split() method is list.

Example

Python
s="internet knowledge hub"
l=s.split()
for x in l:
    print(x)

Output

PowerShell
internet
knowledge
hub

Example

Python
s="22-02-2018" 
l=s.split('-') 
for x in l: 
    print(x)

Output

PowerShell
22
02
2018

Joining of Strings

  • We can join a group of strings (list or tuple) wrt the given separator.
  • seperator.join(group of strings)

Example

PowerShell
my_tuple=('internet','knowledge','hub')
s='-'.join(my_tuple)
print(s)

Output

PowerShell
internet-knowledge-hub

Example

PowerShell
my_list=['internet','knowledge','hub']
s=':'.join(my_list)
print(s)

Output

PowerShell
internet:knowledge:hub

Changing Case of String

  • We can change case of a string by using the following 5 methods.
    • upper() ⇒ To convert all characters to upper case.
    • lower() ⇒ To convert all characters to lower case.
    • swapcase() ⇒ converts all lower case characters to upper case and all upper case characters to lower case.
    • title() ⇒To convert all character to title case. First character in every word should be upper case and all remaining characters should be in lower case.
    • capitalize() ⇒ Only first character will be converted to upper case and all remaining characters can be converted to lower case.

Example

Python
s='learning Python is very Easy'
print(s.upper())
print(s.lower())
print(s.swapcase())
print(s.title())
print(s.capitalize())

Output

PowerShell
LEARNING PYTHON IS VERY EASY
learning python is very easy
LEARNING pYTHON IS VERY eASY
Learning Python Is Very Easy
Learning python is very easy

Checking Starting And Ending Part of String

  • Python contains the following methods for checking start and end word in string.
    • s.startswith(substring)
    • s.endswith(substring)

Example

Python
s='learning Python is very easy'
print(s.startswith('learning'))
print(s.endswith('learning'))
print(s.endswith('easy'))

Output

PowerShell
True
False
True

To Check Type Of Characters in String

  • Python contains the following methods for this purpose.
    • isalnum() ⇒ Returns True if all characters are alphanumeric ( a to z, A to Z, 0 to9 ).
    • isalpha() ⇒ Returns True if all characters are only alphabet symbols (a to z, A to Z).
    • isdigit() ⇒ Returns True if all characters are digits only ( 0 to 9).
    • islower() ⇒ Returns True if all characters are lower case alphabet symbols.
    • isupper() ⇒ Returns True if all characters are upper case alphabet symbols.
    • istitle() ⇒ Returns True if string is in title case.
    • isspace() ⇒ Returns True if string contains only spaces.

Example

Python
print('Internet786'.isalnum())
print('Internet786'.isalpha())
print('Internet'.isalpha())
print('Internet'.isdigit())
print('786786'.isdigit())
print('Internet'.islower())
print('Internet'.islower())
print('abc123'.islower())
print('ABC'.isupper())
print('Learning python is Easy'.istitle())
print('Learning Python Is Easy'.istitle())
print(' '.isspace())

Output

Python
True
False
True
False
True
False
False
True
True
False
True
True

Example

Python
s=input("Enter any character:") 
if s.isalnum(): 
    print("Alpha Numeric Character") 
    if s.isalpha(): 
        print("Alphabet character") 
        if s.islower(): 
            print("Lower case alphabet character") 
        else: 
            print("Upper case alphabet character") 
    else: 
        print("it is a digit") 
elif s.isspace(): 
    print("It is space character") 
else:
    print("Non Space Special Character")

Output

PowerShell
Enter any character:7
Alpha Numeric Character
it is a digit
PowerShell
Enter any character:a
Alpha Numeric Character
Alphabet character
Lower case alphabet character
PowerShell
Enter any character:$
Non Space Special Character
PowerShell
Enter any character:A
Alpha Numeric Character
Alphabet character
Upper case alphabet character

Ungraded Questions

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