Python string functions

capitalize()	Change to upper case for the first char

capitalize() : First char of the input string is converted to upper case

First char is changed to upper case. No parameter is taken by this method.

my_str="welcome to plus2net.com"
print(my_str.capitalize())

Welcome to plus2net.com

center() : Centers the string

my_str="plus2net.com"
print(my_str.center(30))

Output is here ( check the blank space at both sides of the text.

         plus2net.com

casefolod(): Changing to Lower case chars

All chars are changed to lower case

my_str="Welcome to Plus2net Python"
print(my_str.casefold())

Output is here

welcome to plus2net python

count() : Counting the number of presence of a sting

Find out number of occurrence of string inside the main string.

my_str.count(search_string,start,end))

search_string : String to be searched for matching inside main string.
start: Optional , search can be started from this position
end : Optional , search can be ended from this position.

my_str="Welcome to plus2net.com"
print(my_str.count('co'))      # Output is 2
print(my_str.count('co',4))    # Output is 1 
print(my_str.count('co',4,18)) # Output is 0

endswith() : Check if string ends with input string

Check if given string ends with input search_string , returns True if string ends with input search_string otherwise false

my_str.endswith(search_string,start,end))

search_string : String to be checked at the end of the main string.
start: Optional , check to start from this position
end : Optional , check to end from this position.

my_str="Welcome to plus2net.com"
print(my_str.endswith('com')) # Output is True
print(my_str.endswith('com',4,6)) # Output is False
print(my_str.endswith('com',3,6)) # Output is True
print(my_str.endswith('net',16,19)) # Output is True
print(my_str.endswith('net')) # Output is False

expandtabs() : Update the length of Tab

By default expandtabs() ads 8 space by replacing all tab characters. We can set the number of spaces by giving input parameter.

my_str.expandtabs(number))

number : optional , number of space to replace tab character.

my_str='a\tbc\tdef\tghij\tklmno'
my_str=my_str.expandtabs(1)
print(my_str)

The output is here

p l u s 2 n e t . c o m

Change the parameter to higher value and see the result.

my_str='a\tbc\tdef\tghij\tklmno'
my_str=my_str.expandtabs(3)
print(my_str)

Output

a  bc def   ghij  klmno

find() : Search string and get matching position

Check if the search string is within our main string, if found then the position of matching string is returned. If not found then -1 is returned.

my_str.find(search_string,start,end))

search_string : String to be checked inside the main string.
start: Optional , search to start from this position
end : Optional , serch to end from this position.

my_str="Welcome to plus2net.com"
print(my_str.find('co'))      # Output is 3
print(my_str.find('co',4))    # Output is 20 
print(my_str.find('co',4,18)) # Output is -1

We can use index() method also to find the position but find() method returns -1 if not found but index() method raise an exception if not found.

index(): Search string and get matching position

Check if the search string is within our main string, if found then the position of matching string is returned. If not found then this method raise an exception.

my_str.index(search_string,start,end))

search_string : String to be checked inside the main string.
start: Optional , search to start from this position
end : Optional , serch to end from this position.

my_str="Welcome to plus2net.com"
print(my_str.index('co'))      # Output is 3
print(my_str.index('co',4))    # Output is 20 
print(my_str.index('co',4,18)) # ValueError: substring not found

The last line will generate exception.

We can use find() method also to search and find the position but find() method returns -1 if not found but index() method raise an exception if not found.

isalnum() : Check for alphanumeric chars

Checks for alphanumeric characters in a string. Returns true if only number and alphabets are present and returns False if any thing other than alphanumeric characters are present.

my_str='plus2net'
print(my_str.isalnum())      # Output is True

my_str='Welcome to plus2net'
print(my_str.isalnum())      # Output is False (presence of Space)

isalpha(): Check if all chars are alphabet or not

Returns True if all chars are alphabets in a string, Otherwise False is returned.

my_str='plus2net'
print(my_str.isalpha())      # Output is False

my_str='Welcome'
print(my_str.isalpha())      # Output is True

my_str='#1234'
print(my_str.isalpha())      # Output is False

my_str='12.34'
print(my_str.isalpha())      # Output is False

isdecimal(): check if all chars are decimal or not

Returns True if all chars are decimal ( 0 to 9) in a string, Otherwise False is returned.

my_str='12345'
print(my_str.isdecimal())      # Output is True

my_str='234ab'
print(my_str.isdecimal())      # Output is False

my_str='234.45'
print(my_str.isdecimal())      # Output is False

isdigit(): Check if all chars are digit or not

Returns True if all chars are digit in a string, Otherwise False is returned.

my_str='012345'
print(my_str.isdigit())      # Output is True

my_str='12#34'
print(my_str.isdigit())      # Output is False

my_str='abc1234'
print(my_str.isdigit())      # Output is False

my_str='\u0035'              # Unicode of digit 5 
print(my_str.isdigit())      # Output is True

isdigit(): Check if all chars are digit or not

Returns True if all chars are digit in a string, Otherwise False is returned.

my_str='012345'
print(my_str.isdigit())      # Output is True

my_str='12#34'
print(my_str.isdigit())      # Output is False

my_str='abc1234'
print(my_str.isdigit())      # Output is False

my_str='\u0035'              # Unicode of digit 5 
print(my_str.isdigit())      # Output is True

isidentifier() : Check if string is an identifier or not

Returns True if given string is an identifier, otherwise returns False.

What is an identifier?

identifiers can contain chars ( both lower and upper case ), numbers and underscore.
It can’t start with number
It can’t contain space or any other special chars within it.

my_str='_abc45'
print(my_str.isidentifier())      # Output is True

my_str='ab#cd'
print(my_str.isidentifier())      # Output is False ( # not allowed )

my_str='A_abc1234'
print(my_str.isidentifier())      # Output is True

my_str='pq?rs'              
print(my_str.isidentifier())      # Output is False ( ? not allowed)

my_str='pq rs'              
print(my_str.isidentifier())      # Output is False ( space not allowed)

my_str='12ab'              
print(my_str.isidentifier())      # Output is False ( Can't start with number)

islower() : Check if all chars are in lower case or not

Returns True if all chars in a string are in lower case, otherwise rturns False

my_str='_abc45'
print(my_str.islower())      # Output is True

my_str='ab#cd'
print(my_str.islower())      # Output is True

my_str='A_abc1234'
print(my_str.islower())      # Output is False

my_str='pq?rs'              
print(my_str.islower())      # Output is True

my_str='pq rs'              
print(my_str.islower())      # Output is True

my_str='12ab'              
print(my_str.islower())      # Output is True

isnumeric() : Check if all chars of input string are numeric or not

my_str='abc_45'
print(my_str.isnumeric())      # Output is False 

my_str='1234#56'
print(my_str.isnumeric())      # Output is False

my_str='12.34'
print(my_str.isnumeric())      # Output is False

my_str='1234'              
print(my_str.isnumeric())      # Output is True

isprintable() : Check if all chars are printable or not

Returns True if all chars are printable , otherwise False

my_str='Welcome to plus2net'
print(my_str.isprintable())      # Output is False 

my_str='Welcome \t to plus2net'
print(my_str.isprintable())      # Output is False ( presence of Tab \t)

my_str='Welcome to plus2net \n'
print(my_str.isprintable())      # Output is False ( presence of line break \n)

my_str='1234'              
print(my_str.isprintable())      # Output is True

isspace() : Check if all chars are white space or not

Returns True if all chars in a string are white space, otherwise False

my_str='Welcome to plus2net'
print(my_str.isspace())      # Output is False 

my_str='  '
print(my_str.isspace())      # Output is True

my_str=' \n '
print(my_str.isspace())      # Output is True ( presence of line break \n)

my_str='  \t '              
print(my_str.isspace())      # Output is True ( presence of tab \t )

istitle() : Check if all words starts with upper case letters

Returns True if all words starts with Upper Case and other chars are in lower case

my_str='Welcome To Python'
print(my_str.istitle())      # Output is True 

my_str='Welcome to Python'
print(my_str.istitle())      # Output is False

my_str='WELCOME TO PYTHON'
print(my_str.istitle())      # Output is False ( All letters in Upper case )

my_str='Welcome to python'              
print(my_str.istitle())      # False ( All words are not starting with upper case)

isupper() : Check if all chars are in Upper case or not

Returns True if all chars in a string are in Upper case, otherwise returns Fals

my_str='WELCOME TO PYTHON'
print(my_str.isupper())      # Output is True 

my_str='Welcome to Python'
print(my_str.isupper())      # Output is False

join() : Joining elements to form string

String method join can join all elements by using one delimiter. We can apply join method to list, tuple, set and dictionary.

my_list=['Alex','Ronald','John']
output='*'.join(my_list)
print(output) #  Alex*Ronald*John

my_tuple=('Alex','Ronald','John')
output='#'.join(my_tuple)
print(output) #  Alex#Ronald#John

my_set={'Alex','Ronald','John'}
output=' '.join(my_set)
print(output) #  Alex Ronald John

my_dict={'a':'Alex','b':'Ronald','c':'John'}
output='%'.join(my_dict)
print(output) #  a%b%c ( only keys are present ( not values ))

ljust() : left justified string filler

Add left justified filler strings of specified width

my_string.ljust(width, filler)

width : left justified string of width filler : optional, string can be used to fill the width

my_str='Welcome to'
output=my_str.ljust(15,'#')
print(output, 'plus2net')

Output is here

Welcome to##### plus2net

lower() : Change all chars to lowercase

my_str='Welcome to Plus2net'
output=my_str.lower()
print(output)

Output is here

welcome to plus2net

lstrip(): Removes space or chars from left side of the string

By default lstrip() will remove space from left of the string, we can also specify chars to be removed

my_str='    Plus2net'
output=my_str.lstrip()
print(output)

my_str='**plus2net'
output=my_str.lstrip('*')
print(output) # removes * from left

my_str='**## welcome plus2net'
output=my_str.lstrip('*# welcome')
print(output) # removes all left of plus2net

Output is here

Plus2net
plus2net
plus2net

partition() : Break a string into three parts using the input search string

partition() returns a three element tuple by breaking the string using input search string. Three parts here.

1. Left part of the matched string
2. The searched string
3. Right part of the matched string

my_str='Welcome to Plus2net'
output=my_str.partition('to')
print(output)

Output is here

('Welcome ', 'to', ' Plus2net')

We can add one more line to display the last element

print(output[2])

Output

  plus2net

By using partition() method you can separate domain part and userid part of an email address.

replace() : Search and replace string inside a main string

Search for a string inside a main string and if found then replace it with another string

main_string.replace(search_string, replace_string, count)

search_string: Required , string to search within main string
replace_string: Required, string to replace if matching is found
count: Number of times the replacement to happen. By default all matches will be replaced.

my_str='Welcome to PHP section of  plus2net'
output=my_str.replace('PHP','Python')
print(output)

my_str='Welcome to PHP section of  plus2net. PHP has many buit-in functions'
output=my_str.replace('PHP','Python')
print(output)

my_str='Welcome to PHP section of  plus2net. PHP has many buit-in functions'
output=my_str.replace('PHP','Python',1)
print(output)

my_str='Welcome to PHP section of  plus2net'
output=my_str.replace('MySQL','Python')
print(output) # Nothing replaced as no matching found

Output is here

Welcome to Python section of  plus2net
Welcome to Python section of  plus2net. Python has many buit-in functions
Welcome to Python section of  plus2net. PHP has many buit-in functions
Welcome to PHP section of  plus2net

rfind():Find the rightmost matching of search string and return the position

Returns the rightmost matching position of the search string in a main string

main_string.rfind(search_string, start, end)

search_string : Required, String to be searched and position is returened if found.
start : Optional, Starting position of search , by default it is from 0 or starting position of string
end : Optional , ending position of search, by default it is end of the string.

my_str='Welcome to plus2net.com Python section'
output=my_str.rfind('co') 
print(output) # output is 20

my_str='Welcome to plus2net.com Python section'
output=my_str.rfind('co',10,21)
print(output) # output is -1


my_str='Welcome to plus2net.com Python section'
output=my_str.rfind('co',10,22)
print(output) # output is 20

Output is here

20
-1
20

If the searched string is not found then -1 is returned by rfind() method, however rindex() method raise an exception if not found

rindex():Find the rightmost matching of search string and return the position

Returns the rightmost matching position of the search string in a main string

main_string.rindex(search_string, start, end)

my_str='Welcome to plus2net.com Python section'
output=my_str.rindex('co') 
print(output) # output is 20

my_str='Welcome to plus2net.com Python section'
output=my_str.rindex('co',10,22)
print(output) # output is 20

my_str='Welcome to plus2net.com Python section'
output=my_str.rindex('co',10,21)
print(output) # output is -1

Output

20
20
Traceback (most recent call last):
  File "D:/my_py/string-rindex.py", line 10, in 
    output=my_str.rindex('co',10,21)
ValueError: substring not found

rindex() method raise an exception if searched string is not found but rfind() returns -1 if searched string is not found. That is the main difference between rfind() and rindex()

rjust(): Right align the string by using another string as filler

Returns right aligned string with filler char, by default space is used as filler.

my_str.rjust(length,filler)

length : length of the string required filler : Optional, char can be used to fill the length after right justify. Blank space is used by default.

my_str='Welcome to'
output=my_str.rjust(15,' ')
print(output, 'plus2net')

Output

     Welcome to plus2net

my_str='Welcome to'
output=my_str.rjust(15,'#')
print(output, 'plus2net')

output

#####Welcome to plus2net

rpartition() : Break a string into three parts using the input search string

partition() returns a three element tuple by breaking the string using input search string. Three parts are here.

1. Left part of the matched string
2. The searched string
3. Right part of the matched string

my_str='Welcome to Plus2net'
output=my_str.rpartition('to')
print(output)

Output is here

('Welcome ', 'to', ' Plus2net')

We can add one more line to display the last element

print(output[2])

Output

  plus2net

If matching string is not found then rpartition() returns the tuple with 3rd element as full string.

my_str='Welcome to Plus2net'
output=my_str.rpartition('ab')
print(output)

Output is here

('', '', 'Welcome to Plus2net')

If we use partition() in place or rpartition() the output is here ( the difference between rpartition() and partition() )

('Welcome to Plus2net', '', '')

rsplit(): split the string by using delimiter

rsplit() returns a list after breaking a string using delimiter and max value

my_str.rsplit(delimiter,max_value)

delimiter : required, to be used to break the string
max_value : optional , the number of elements in output plus one. Default value is -1 so it includes all occurance.

my_list="'Alex','Ronald','John'"
my_list=my_list.rsplit(',')
print(my_list)

my_list="'Alex','Ronald','John'"
my_list=my_list.rsplit(',',1)
print(my_list)

output

["'Alex'", "'Ronald'", "'John'"]
["'Alex','Ronald'", "'John'"]

rstrip(): Removes space or chars from right side of the string

By default rstrip() will remove space from right of the string, we can also specify chars to be removed

my_str='Plus2net    '
output=my_str.rstrip()
print(output)

my_str='plus2net**'
output=my_str.rstrip('*')
print(output) # removes * from right

my_str='plus2net *#*#'
output=my_str.rstrip('*#')
print(output) # removes all right

Output is here

plus2net
plus2net
plus2net

split(): split the string by using delimiter

split() returns a list after breaking a string using delimiter and max value

my_str.split(delimiter,max_value)

delimiter : required, to be used to break the string
max_value : optional , the number of elements in output plus one. Default value is -1 so it includes all occurance.

my_list="'Alex','Ronald','John'"
my_list=my_list.split(',')
print(my_list)

my_list="'Alex','Ronald','John'"
my_list=my_list.split(',',1)
print(my_list)

output

["'Alex'", "'Ronald'", "'John'"]
["'Alex'", "'Ronald','John'"]

By using rsplit() in place of split(), the output will change like this. ( diference betweeen rsplit() and split() )

["'Alex'", "'Ronald'", "'John'"]
["'Alex','Ronald'", "'John'"]

splitlines(): split the string by using line breaks as delimiter

splitlines() returns a list after breaking a string using line breaks as delimiter

my_str.splitline(keeplinebreaks)

keeplinebreaks : optional, True or False, by default it is False for not retaining line breaks Output

my_str='Welcome\n to\n Plus2net'
output=my_str.splitlines()
print(output)

my_str='Welcome\n to\n Plus2net'
output=my_str.splitlines(True)
print(output)

Output is here

['Welcome', ' to', ' Plus2net']
['Welcome\n', ' to\n', ' Plus2net']

startswith():Check if the string starts with specified string or not

Returns True if the main string starts with specified search string, otherwise returns False

main_string.startswith(search_string, start, end)

search_string : Required, String to be searched to check to match starting of the main string.
start : Optional, Starting position of search , by default it is from 0 or starting position of string
end : Optional , ending position of search, by default it is end of the string.

my_str='Welcome to plus2net.com Python section'
output=my_str.startswith('Wel') 
print(output) # output is True

my_str='Welcome to plus2net.com Python section'
output=my_str.startswith('co',3)
print(output) # output is True


my_str='Welcome to plus2net.com Python section'
output=my_str.startswith('co',20,24)
print(output) # output is True

Output is here

True
True
True

strip(): Removes space or chars from left & right side of the string

By default strip() will remove space from left(leading) and right(trailing) of the string, we can also specify chars to be removed

my_str='  Plus2net    '
output=my_str.strip()
print(output)

my_str='*****plus2net**'
output=my_str.strip('*')
print(output) # removes * from both sides

my_str='*#*# plus2net *#*#'
output=my_str.strip('*# ')
print(output) # removes * ,# and space from both sides

Output is here

plus2net
plus2net
plus2net

swapcase(): Upper case chars to Lower case and and vice versa

All upper case chars are changed to lower case and lower case chars are changed to upper case

my_str='Welcome to plus2net Python Section'
output=my_str.swapcase()
print(output)

Output is here

wELCOME TO PLUS2NET pYTHON sECTION

title(): Change First letter of each word to upper case

my_str='welcome to plus2net python section'
output=my_str.title()
print(output)

my_str='welcome #id 15of  plus2net'
output=my_str.title()
print(output)

Output

Welcome To Plus2Net Python Section
Welcome #Id 15Of  Plus2Net

This also changes the first char after any number of special chars ( check plus2Net )

translate() , maketrans() : Search replace and delete of set of chars.

str_update=str_input.maketrans(str_search,str_replace,str_delete)

str_search : Required, Chars to be searched
str_replace: Required, Chars to be replaced ( mapped to searched chars )
str_delete : Optional, Chars to be replaced with None ( deleted in final string )

Length of str_search should be equal to length of str_replace
the method maketrans() returns a dictionary ( str_update ) with chars mapped for search and replace and this can be used for translate().

str_search='abc'  # search chars 
str_replace='xyz' # replace chars 
str_delete='pqr'  # delete chars 

str_input='abcdefghpqr' #input string 

str_update=str_input.maketrans(str_search,str_replace,str_delete)

print(str_update) # dictionary output with chars mapped. 
print("input string : ",str_input)
print("Output string: ",str_input.translate(str_update))

Output

{97: 120, 98: 121, 99: 122, 112: None, 113: None, 114: None}
input string :  abcdefghpqr
Output string:  xyzdefgh

upper(): All chars changed to Upper case

All chars are changed to upper case letters , no parameter is taken by this mehod.

my_str='Welcome to plus2net Python section'
output=my_str.upper()
print(output)

Output

WELCOME TO PLUS2NET PYTHON SECTION

zfill(): Fill the string with zeros

Fill zeros upto the input length of the string

my_str='plus2net'
output=my_str.zfill(15)
print(output)

my_str='25'
output=my_str.zfill(5)
print(output)

output is here

0000000plus2net
00025

Exercise on String methods
Display one input string after adding x zeros, where x is equal to half of the length of the string
Read one html page ( use one sample page ) and display the content written inside different tags like <Title>, <Description>, <keyword>, <body> etc . ( View source of any web page will show you different tags )
You can use sample html page here
What is the difference between rfind() and rindex()
Input string is 'Welcome to plus2net.com'. Replace the .com with .net
Find out the number of occurrence ( frequency ) of each chars in a string
Create a string by suing first two chars , last two chars and middle two ( or three based on centre ) chars of a input string.
From one input string char with highest occurrence ( frequency ) should be replaced by its number of occurrence
Take one input string and generate error message if any special char including space is present. Under score is allowed. Add extension of .com to this string and display.
Arrange one input string in such a way that Upper case letters should come first
Change to upper case all the chars at even index position
Collect the following details . Title , description, keywords , body , H1, Details and then create one html page and save as my_name.html
Insert second string at the centre of the first string
Create Caesar encryption of an input string
Convert first n chars to upper case
Find out the first repeated char in a string
Change to upper case char for all first and last char of words present inside a string
Count number of special chars, upper case , lower case and numbers present in a string
Collect the integer part from the string.
Input = I joined college at 18 years of age
Output = 18

if else for loop

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String methods in Python

capitalize() : First char of the input string is converted to upper case

center() : Centers the string

casefolod(): Changing to Lower case chars

count() : Counting the number of presence of a sting

endswith() : Check if string ends with input string

expandtabs() : Update the length of Tab

find() : Search string and get matching position

index(): Search string and get matching position

isalnum() : Check for alphanumeric chars

isalpha(): Check if all chars are alphabet or not

isdecimal(): check if all chars are decimal or not

isdigit(): Check if all chars are digit or not

isdigit(): Check if all chars are digit or not

isidentifier() : Check if string is an identifier or not

islower() : Check if all chars are in lower case or not

isnumeric() : Check if all chars of input string are numeric or not

isprintable() : Check if all chars are printable or not

isspace() : Check if all chars are white space or not

istitle() : Check if all words starts with upper case letters

isupper() : Check if all chars are in Upper case or not

join() : Joining elements to form string

ljust() : left justified string filler

lower() : Change all chars to lowercase

lstrip(): Removes space or chars from left side of the string

partition() : Break a string into three parts using the input search string

replace() : Search and replace string inside a main string

rfind():Find the rightmost matching of search string and return the position

rindex():Find the rightmost matching of search string and return the position

rjust(): Right align the string by using another string as filler

rpartition() : Break a string into three parts using the input search string

rsplit(): split the string by using delimiter

rstrip(): Removes space or chars from right side of the string

split(): split the string by using delimiter

splitlines(): split the string by using line breaks as delimiter

startswith():Check if the string starts with specified string or not

strip(): Removes space or chars from left & right side of the string

swapcase(): Upper case chars to Lower case and and vice versa

title(): Change First letter of each word to upper case

translate() , maketrans() : Search replace and delete of set of chars.

upper(): All chars changed to Upper case

zfill(): Fill the string with zeros

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