Data Structure & Algorithms | String in Python

A string is a data type in programming that represents a sequence of characters. In Python, strings are represented using the str class. Strings are immutable in Python, which means that once a string is created, its contents cannot be modified.

To create a string in Python, you can simply enclose a sequence of characters in single quotes (‘’) or double quotes (“”).

my_string = 'Hello, world!'

Some common operations that can be performed on strings include concatenation (joining two or more strings together), slicing (extracting a portion of a string), and searching for a substring within a string.

Python provides several built-in methods for working with strings, such as the len() function (which returns the length of a string), the lower() method (which returns a copy of a string with all characters in lowercase), the upper() method (which returns a copy of a string with all characters in uppercase), and the split() method (which splits a string into a list of substrings based on a delimiter).

# Concatenation
first_name = 'John'
last_name = 'Doe'
full_name = first_name + ' ' + last_name
print(full_name)  # Output: John Doe

# Slicing
my_string = 'Hello, world!'
substring = my_string[0:5]
print(substring)  # Output: Hello

# Searching
my_string = 'Hello, world!'
if 'world' in my_string:
    print('Found it!')  # Output: Found it!

# Length
my_string = 'Hello, world!'
length = len(my_string)
print(length)  # Output: 13

# Lowercase
my_string = 'Hello, world!'
lowercase = my_string.lower()
print(lowercase)  # Output: hello, world!

# Uppercase
my_string = 'Hello, world!'
uppercase = my_string.upper()
print(uppercase)  # Output: HELLO, WORLD!

# Splitting
my_string = 'Hello, world!'
words = my_string.split(',')
print(words)  # Output: ['Hello', ' world!']

There are several algorithms that can be applied to strings in Python, depending on what you’re trying to accomplish.

Reverse a string

You can reverse a string in Python using slicing.

my_string = 'Hello, world!'
reversed_string = my_string[::-1]
print(reversed_string)  # Output: !dlrow ,olleH

Occurrences of a substring

You can use the count() method to count the number of occurrences of a substring within a string.

my_string = 'Hello, world!'
count = my_string.count('l')
print(count)  # Output: 3

String is a palindrome

You can check if a string is a palindrome (i.e., reads the same backwards as forwards) by comparing the string to its reverse.

my_string = 'racecar'
reversed_string = my_string[::-1]
if my_string == reversed_string:
    print('It's a palindrome!')  # Output: It's a palindrome!