Methods and Functions

Python reversed()

In python, we can retrieve the reverse of a number, a string, a list, and so on. The python reverse() function returns the sequence’s reversed order.

For example:

Input: str = I love coding in python

Output: str = python in coding love I 

The syntax for the same is:

reversed(seq)

python reverse

Source Code

reversed() Parameters

The reversed function in python takes one argument as the input. 

seq-this is the sequence that must be reversed. 

Return value from reversed()

After implementing the reversed() in python, the reversed order of the given sequence will be returned. 

Example 1: Using reversed() in the string, tuple, list, and range

We used the list() method to convert the iterators returned by reversed() to a list in our example.

Source Code

                    

# for string

seqstring11 = 'Python'

print(list(reversed(seq_string)))



# for tuple

seqtuple11 = ('P', 'y', 't', 'h', 'o', 'n')

print(list(reversed(seq_tuple)))



# for range

seq_range = range(5, 9)

print(list(reversed(seq_range)))



# for list

seq_list = [1, 2, 4, 3, 5]

print(list(reversed(seq_list)))

Output

['n', 'o', 'h', 't', 'y', 'P']

['n', 'o', 'h', 't', 'y', 'P']

[8, 7, 6, 5]

[5, 3, 4, 2, 1]



Example 2: reversed() in custom objects


class Vowels:

    vowels11 = ['a', 'e', 'i', 'o', 'u']



    def __reversed__(self):

        return reversed(self.vowels11)



v = Vowels()

print(list(reversed(v)))

Output

['u', 'o', 'i', 'e', 'a']

 

Is there a reverse function in Python?

Yes, the reversed() function allows us to reverse the order of items in a sequence. It takes a sequence as input and outputs an iterator. 

For example:

The algorithm of the program is given below:

 

  1. Using the split() function of the string data type in Python, separate each word in a given string.
  2. Reverse the list of words in the list. After combining each word with a space using ” “, print the list’s words as a string using the join() in python.

Source Code:

                    

def rev_sentence(sentence): 

  

    # First, break the string into words. 

    words1 = sentence.split(' ') 

  

# We need to reverse the list 

# using the split function and join 

# them using the space function

    reverse_sentence = ' '.join(reversed(words1)) 

  

    #return reverse sentence from the joined string

  

if __name__ == "__main__": 

    input = 'geeks quiz practice code'

    print (rev_sentence(input))



Output:

code practice quiz geeks

What is the reversed word in Python?

Example

                    

#creating the string



strg1 = "I am an expert python programmer"



# splitting the string on space

words1 = strg1.split()



# reversing the words using reversed() function



words1 = list(reversed(words))



# joining the words and printing

print(" ".join(words1))



Output



programmer python an am I expert

How do you reverse a number in Python?

                    

number = int(input("Enter the integer number: "))  

  

# Initiate value to null  

revs_number = 0  

  

# Using the while loop, reverse the integer number. 

  

while (number > 0):  

    # Logic applied for the program 



    remainder = number % 10  

    revs_number = (revs_number *10) + remainder  

    number = number // 10  

  

# Display the result  

print("The reverse number is : {}".format(revs_number))  



Output:

Enter the integer number: 12345

The reverse number is: 54321

How do you reverse a list in Python 3?

In the Python programming language, we can reverse a list using three methods. The three methods are:

  • Reverse the list using slicing
  • Reverse the list using Reverse()
  • Reverse the list using Reversed

 

Reversing the given list with the help of the slicing:

We declared our variable studentNames11 and then constructed a slice function to reverse the list in our code. This is a popular method of slicing lists. However, it is inefficient because it duplicates the list, which consumes memory. In addition, compared to other methods of reversing lists, this function can be a little more advanced.

Example:

                    

studentNames11 = ["Hannah", "Imogen", "Lewis", "Peter", "Zayn", "Louis", "Harry"]

print(studentNames11[::-1])


Output:


["Harry", "Louis", "Zayn", "Peter", "Lewis", "Imogen", "Hannah"]

Example for reversing the program using the reverse()

The second method is to use the built-in reverse function (). To reverse the contents of a list object in-place, use the reverse() function. You will not be generating a new list as a result of this. Instead, we’ll make changes to the original list object.

Source Code:

                    

list1 = ['physics', 'Biology', 'chemistry', 'maths']

list1.reverse()

print ("list now : ", list1)


Output

list now : ['maths', 'chemistry', 'Biology', 'physics']

Example: For reversing list using the reversed function

                    

studentNames2 = ["Harry", "Ron", "Hermoine"]



for j in reversed(studentNames2):

print(j)



Output



"Hermoine"

"Ron"

"Harry"

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