Question

Write a python program to input a string and print it in the reverse order without creating a new string.

[[ strings in python]]

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Answer 1

Answer:

In Python, strings are ordered sequences of character data.

There is no built-in method to reverse a string. However, strings can be reversed in several different ways.

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Methods

Three methods to reverse a string are explained below:

1. Slicing

Strings can be reversed using slicing. To reverse a string, we simply create a slice that starts with the length of the string, and ends at index 0.

To reverse a string using slicing, write:

stringname[stringlength::-1] # method 1  

Or write without specifying the length of the string:

stringname[::-1] # method2

The slice statement means start at string length, end at position 0, move with the step -1 (or one step backward).

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str="Python" # initial string

stringlength=len(str) # calculate length of the list

slicedString=str[stringlength::-1] # slicing  

print (slicedString) # print the reversed string

2. Loop

To start, let’s create a new array called reversedString[].

We can then loop over the list with iterating variable index initialized with the length of the list.

In each iteration, concatenate value of str[index-1] with reverseString

Decrement the index.

We then simply keep iterating until the index is less than zero.

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str = "Python" # initial string

reversedString=[]

index = len(str) # calculate length of string and save in index

while index > 0:  

   reversedString += str[ index - 1 ] # save the value of str[index-1] in reverseString

   index = index - 1 # decrement index

print(reversedString) # reversed string

3. Use join

This is a powerful technique that takes advantage of Python’s iterator protocol. This technique reverses a string using reverse iteration with the reversed() built-in function to cycle through the elements in the string in reverse order and then use .join() method to merge all of the characters resulting from the reversed iteration into a new string.

The general syntax is

str="Python"  

reversedstring=''.join(reversed(str))

The following Python code demonstrates the concept.

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str = 'Python' #initial string

reversed=''.join(reversed(str)) # .join() method merges all of the characters resulting from the reversed iteration into a new string

print(reversed) #print the reversed string