4.4. String Methods

The str data type provides many useful methods that can be used to manipulate a string.

Note

A method is a function that can be called on a specific data type. This concept is covered in detail later in the guide.

This section lists some of the commonly used and useful ones available on a string.

Case Methods

These methods are used to change the case of a string:

Method	Description
`str.upper()`	Converts the string to all upper case.
`str.lower()`	Converts the string to all lower case.
`str.capitalize()`	Changes first character of string to upper case.
`str.swapcase()`	Changes lowercase characters to uppercase and vice versa.
`str.title()`	Changes first character of each word in string to upper case.

CodeOutput

string = input('Enter some text: ')

print('upper:', string.upper())
print('lower:', string.lower())
print('capitalize:', string.capitalize())
print('swapcase:', string.swapcase())
print('title:', string.title())

Enter some text: welcome to Python
upper: WELCOME TO PYTHON
lower: welcome to python
capitalize: Welcome to Python
swapcase: WELCOME TO pYTHON
title: Welcome To Python

str.endswith() & str.startswith()

endswith() and startswith() is used to check whether a string begins with a specific string.

CodeOutput (input: Hello)Output (input: Hello?)

text = input('Enter a text: ')
print('Question?', text.endswith('?'))

if text.endswith('?'):
    print('You entered a question.')

Enter a text: Hello
Question? False

Enter a text: Hello?
Question? True
You entered a question.

They take two optional arguments:

start defines the starting index. By default, this is 0 (start of string)
end defines the ending index. By default, this is length of string (end of string)

CodeOutput

text = 'fruits: apple, strawberry, peach'

# searches from 8th index until end of string
print(text.startswith('apple', 8))

# searches from 8th index to 25th index (exclusive)
print(text.endswith('strawberry', 8, 25))

True
True

str.replace()

str.replace() is used to replace a certain substring in a string with another string. str.replace(old, new) replaces old with new.

replace() returns a new string with old substring replaced.

CodeOutput

text = 'Hello, World!'
new = text.replace('Hello', 'Bye')
print(new)

Bye, World!

This method replaces all occurences of given string with new one but could take a count argument to indicate the number of occurences to replace.

CodeOutput

text = 'apple, peach, strawberry, apple, banana, apple'
all_replaced = text.replace('apple', '[apple]')
one_replaced = text.replace('apple', '[apple]', 1)
print(all_replaced)
print(one_replaced)

[apple], peach, strawberry, [apple], banana, [apple]
[apple], peach, strawberry, apple, banana, apple

str.count()

str.counts() counts the number of times a substring has occured in a string.

CodeOutput

text = 'apple, peach, strawberry, apple, banana, apple'
print(f'apple occured {text.count("apple")} times')

apple occured 3 times

This method takes optional start and end parameters indicating the starting position to search from and ending position to end search at.

text.count('apple', 7) starts searching from 7th index, text.count('apple', 7, 14) searches between 7th and 14th (exclusive) position.

CodeOutput

text = 'apple, peach, strawberry, apple, banana, apple'
print(f'apple occured {text.count("apple", 7)} times after 7th index')
print(f'apple occured {text.count("apple", 0, 32)} times between first and 32nd index')

apple occured 2 times after 7th index
apple occured 2 times between first and 32nd index

In above code, the first output shows the number of occurences after first occurence and second output shows number of occurences except the last one.

Validation Methods

Some methods provided by strings are used for validation of the string. These are listed below:

Method	Description
`str.isalpha()`	Checks if all characters in the string are alphabet letters.
`str.isalnum()`	Checks if all characters in string are alphanumeric.
`str.isdigit()`	Checks if all characters in string are digits or integers.
`str.isidentifier()`	Checks if the string is a valid variable name.
`str.isnumeric()`	Checks if all characters in string are numeric.
`str.isspace()`	Checks if all characters in string are blank spaces.
`str.istitle()`	Checks if all words in the string start with a capital letter.
`str.isupper()`	Checks if all characters in the string are uppercase.
`str.isupper()`	Checks if all characters in the string are lowercase.

Methods listed above don't take any additional parameters.

Example:

CodeOutput

text1 = 'HELLO'
text2 = 'Hello'
print(text1.isupper())
print(text2.isupper())

True
False

There are many other methods provided by the str data type and all of them cannot be listed here. For a list of all methods, check the official Python documentation on this topic.