String Methods

In this article, we review several useful Python string methods that create new strings from a source string without modifying the original. These methods are essential for effective string manipulation in your Python projects and can help you build cleaner and more readable code.

Capitalize

The capitalize method converts the first character of the string to uppercase (if it's alphabetical) and converts all remaining characters to lowercase.

Example usage:

print('hello world!'.capitalize())
print('12 bananas'.capitalize())
print('αβγδ'.capitalize())
print(' Hello!'.capitalize())

Expected output:

Hello world!
12 bananas
Αβγδ
hello!

Center

The center method returns a new string padded with spaces or an optional specified character. The first parameter represents the total width of the resulting string.

Example usage:

print('hello'.center(9))
print('hello'.center(9, '*'))
print('1234'.center(10, '0'))
print('1234'.center(10))

Expected output:

  hello  
**hello**
0001234000
   1234

Combined Example for Capitalize and Center

The following example demonstrates using both the capitalize and center methods in a single script:

# main.py
print('hello world!'.capitalize())
print('12 bananas'.capitalize())
print('αβγδ'.capitalize())
print(' Hello!'.capitalize())

print('hello'.center(9))
print('hello'.center(9, '*'))
print('1234'.center(10, '0'))
print('1234'.center(10))

Console output:

Hello world!
12 bananas
Αβγδ
hello!
  hello  
**hello**
0001234000
   1234

Endswith and Startswith

The endswith and startswith methods are used to verify whether a string ends or begins with a specified substring, respectively. Both methods return True or False.

Example usage:

print('hello world!'.endswith('!'))
print('hello world!'.endswith('world!'))
print('hello world!'.endswith('hello'))
print('hello world!'.endswith('world'))

print('hello world!'.startswith('hello'))
print('hello world!'.startswith('Hello'))
print('hello world!'.startswith('h'))
print('hello world!'.startswith('world'))

Expected output:

True
True
False
False
True
False
True
False

Find and rfind

The find method returns the index of the first occurrence of a substring, and it returns -1 if the substring is not found. You can also specify start and end indices for the search. Conversely, the rfind method searches from the right side of the string.

Example usage:

print('hello world!'.find('h'))
print('hello world!'.find('world'))
print('hello world!'.find('o'))
print('hello world!'.find('x'))
print('hello world!'.find('r', 4, 10))
print('hello world!'.find('r', 1, 4))
print('hello world!'.find('h', 3))

Searching from the right:

print('hello world!'.rfind('o'))

Alphanumeric, Alphabetic, and Digit Checks

Python provides several methods to check the composition of strings:

• isalnum(): Returns True if all characters are alphanumeric.
• isalpha(): Returns True if all characters are letters.
• isdigit(): Returns True if all characters are digits.

Example usage:

print('python'.isalnum())
print('[email protected]'.isalnum())

print('Hello world!'.isalpha())
print('Hello'.isalpha())

print('1998'.isdigit())
print('1998/04/06'.isdigit())

Expected output:

True
False
False
True
True
False

Case and Whitespace Checks

The following methods are used to verify the case of characters or the presence of whitespace:

• islower(): Returns True if all alphabetic characters are lowercase.
• isupper(): Returns True if all alphabetic characters are uppercase.
• isspace(): Returns True if the string consists solely of whitespace characters.

Example usage:

print('hello world'.islower())
print('Hello world'.islower())

print('hello world'.isupper())
print('HELLO WORLD'.isupper())

print('hello world'.isspace())
print(' '.isspace())

Expected output:

True
False
False
True
False
True

Join and Split

Join

The join method concatenates an iterable of strings using the string on which it is invoked as a separator. Ensure every element in the list is a string.

Example usage:

print(' '.join(['apple', 'kiwi', 'pear']))
print('!'.join(['apple', 'kiwi', 'pear']))
print(''.join(['apple', 'kiwi', 'pear']))

Expected output:

apple kiwi pear
apple!kiwi!pear
applekiwipear

Split

The split method breaks a string into a list of substrings using a specified delimiter. If no delimiter is provided, it splits the string at whitespace.

Example usage:

print('apple kiwi pear'.split())
print('apple n kiwi n pear'.split())
print('apple kiwi pear'.split('kiwi'))

Expected output:

['apple', 'kiwi', 'pear']
['apple', 'kiwi', 'pear']
['apple ', ' pear']

Lower and Upper

The lower method converts all uppercase letters in a string to lowercase, while the upper method converts all lowercase letters to uppercase.

Example usage for lowercase conversion:

print('Hello world!'.lower())
print('lowercase already'.lower())
print('User Input'.lower())

Expected output:

hello world!
lowercase already
user input

Example usage for uppercase conversion:

print('Hello world!'.upper())
print('UPPERCASE ALREADY'.upper())
print('User Input'.upper())

Expected output:

HELLO WORLD!
UPPERCASE ALREADY
USER INPUT

Stripping Whitespace and Characters

Python provides three primary methods to remove characters from strings:

• lstrip(): Removes leading whitespace or specified characters.
• rstrip(): Removes trailing whitespace or specified characters.
• strip(): Removes both leading and trailing whitespace or specified characters.

Using lstrip

Example usage:

print(' Hello world!'.lstrip())
print('www.kodekloud.com'.lstrip('w.'))

Expected output:

Hello world!
kodekloud.com

Using rstrip

Example usage:

print('Hello world! '.rstrip())
print('www.kodekloud.com'.rstrip('.com'))

Expected output:

Hello world!
www.kodekloud

Using strip

Example usage:

print(' Hello world! '.strip())
print('*123456789000'.strip('0'))

Expected output:

Hello world!
*123456789

Replace, Swapcase, and Title

Replace

The replace method generates a new string by replacing all occurrences of a specified substring with another substring. You can also limit the number of replacements by providing an optional third parameter.

Example usage:

print('That is great'.replace('great', 'bad'))
print('123456789'.replace('123', ''))
print('Replace all spaces'.replace(' ', '-'))

Expected output:

That is bad
456789
Replace-all-spaces

Swapcase

The swapcase method swaps the case of each letter in the string, so uppercase becomes lowercase and vice versa.

Example usage:

print('I am SO happy!'.swapcase())

Expected output:

i AM so HAPPY!

Title

The title method capitalizes the first character of every word and converts the rest to lowercase.

Example usage:

print('python has GREAT methods!'.title())

Expected output:

Python Has Great Methods!

That concludes our comprehensive guide on Python string methods. Start practicing these methods in your coding exercises and projects to improve your string manipulation skills. For more Python tutorials and examples, check out additional Python documentation.