Replace Occurrences by K Except First Character in Python

Python has in build functions like slicing() and replace() that can be used for replacing the occurrence by k except the first character.

In Python, strings are among the most often used types. These are easily made by simply surrounding letters in quotations. Python treats single quotes and double quotes the same way. Assigning a value to a variable and creating a string is really straightforward.

Example

Assume we have taken an input string and k. We will now replace all the k characters except the first in an input string with the input character using the above methods.

Input

inputString = 'blueforblueforblue'

Output

Resultant string after replacing:  bluefor*luefor*lue

Using slicing and replace() functions

In this method we are going to use the combination of slicing and replace function to replace the occurrence. The replace function returns a copy of the string that replaces all occurrences of an old substring with another new substring.

Syntax

string.replace(old, new, count)

Algorithm (Steps)

Following are the Algorithm/steps to be followed to perform the desired task -.

• Create a variable to store the input string.

• Print the input string.

• Create another variable to store input k character for replacing.

• Slice from the second character to the end of the string and replace the occurrences of the first character with the given symbol k.

• Concatenate this result with the first character.

• Print the resultant string after replacing it.

Example 1

The following program returns a string after replacing the occurrences by k except the first character using slicing and replace() functions -

# input string
inputString = 'blueforblueforblue'
# printing input string
print("Input string: ", inputString)
# input K character for replacing 
k  = '*'
# replacing all the characters except the first character with the given k symbol
resultantStr = inputString[0] + inputString[1:].replace(inputString[0], k)
# printing the resultant string after replacing 
print("Resultant string after replacing: ", resultantStr)

Output

On executing, the above program will generate the following output -

Input string:  blueforblueforblue
Resultant string after replacing:  bluefor*luefor*lue

Example 2

The following program returns a string after replacing the occurrences by k except the first character using replace() functions -

# input string
inputString = 'blueforblueforblue'
# printing input string
print("Input string: ", inputString)
# input K character for replacing
k = '*'
# Replacing using the replace() method
resultantStr = inputString.replace(
    inputString[0], k).replace(k, inputString[0], 1)
# printing the resultant string after replacing
print("Resultant string after replacing: ", resultantStr)

Output

On executing, the above program will generate the following output -

Input string:  blueforblueforblue
Resultant string after replacing:  bluefor*luefor*lue

Using for loop

In this method we are going to take help of for loop and not operator of python to replace the occurrence by k except the first character. The not operator is aa logical operator that returns True if the statement/statements are not True else returns False.

Algorithm (Steps)

Following are the Algorithm/steps to be followed to perform the desired task -.

• Create a variable to store the input string.

• Print the input string.

• Create another variable to store input k character for replacing

• Initialize an empty string for storing the resultant string.

• Use the for loop to traverse through each character of an input string.

• Use the if conditional statement to check whether the current character is equal to the first character of the input string with indexing and whether it is NOT present in the resultant string using the not operator.

• Add that current character to the resultant string using the +(Concatenation) operator if the condition is true.

• Use the elif conditional statement to check whether the current character is equal to the first character of the input string and whether it is present in the resultant string

• Add input k to the resultant string using the + operator if the condition is true.

• Else add the current character directly to the resultant string without modification.

• Print the resultant string after replacing

Example

The following program returns a string after replacing the occurrences by k except the first character using for loop -

# input string
inputString = 'blueforblueforblue'
# printing input string
print("Input string: ", inputString)
# input K character for replacing 
k  = '*'
# initilazing empty string for storing resultant string 
resultantStr= ""
# travsering through each character of an input string 
for c in inputString:
    # checking whether the current character is equal to the first character  
    # of the input string and it is NOT present in the resultant string
	if c==inputString[0] and c not in resultantStr:
        # add that current character to the resultant string  
		resultantStr+=c
    # checking whether the current character is equal to the first character  
    # of the input string and it is in the resultant string
	elif c==inputString[0] and c in resultantStr:
        # adding k to the  resultant string  
		resultantStr+=k
	else:
        # else adding that character directly without modifying
		resultantStr+=c
# printing the resultant string after replacing 
print("Resultant string after replacing: ", resultantStr)

Output

On executing, the above program will generate the following output -

Input string:  blueforblueforblue
Resultant string after replacing:  bluefor*luefor*lue

Conclusion

In this article we have learned how to Replace occurrences by K except first character using 3 different approaches. We learned how to use the slicing to slice across the string and replace its elements. Additionally, we learnt how to join or combine two strings using the concatenation operator (+).