Case Insensitive String Replacement Using Python Program

In this article, we will learn Case insensitive string replacement in python.

Methods Used

The following are the various methods to accomplish this task ?

• Using re.IGNORECASE, re.escape(), re.sub()

• Using re.sub(), lambda, re.escape() functions

• Using split(), lower() & replace() functions

• Using split(), list() and join() functions

Method 1: Using re.IGNORECASE, re.escape(), re.sub()

re.compile() function

A regular expression pattern can be combined with pattern objects, which can then be used for pattern matching. This function also allows searching for a pattern again without rewriting it.

Syntax

re.compile(pattern, repl, string)

re.sub() function

The string with replaced values is returned by the re.sub() function, which stands for a substring. When we use this function, we can replace several elements with a list.

Syntax

re.sub(pattern, repl, string, count=0, flags=0)

re.escape() function

This function returns a string with all non-alphanumerics backslashed. If you want to match an arbitrary literal string that might contain regular expression metacharacters this function can be used.

Algorithm (Steps)

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

• Use the import keyword to import the re(regex) module.

• Create a variable to store the input string.

• Print the input string.

• Create another variable to store the input replace string to be replaced with.

• Initialize a substring to be replaced.

• Ignore all the cases of the given string using the compile(), escape(), and IGNORECASE attributes (re.IGNORECASE is used to ignore cases).

• Substitute the substring with replacing a string using the regex sub() function

• Print the resultant string after replacing the case-insensitively.

Example

The following program returns a string after case-insensitive string replacement using re.IGNORECASE, re.escape(), re.sub() functions -

# importing re(regex) module
import re

# input string
inputString = "hello TuTorialsPOint python"

# printing input string
print("Input String: ", inputString)

# input replace string to be replaced with
replaceString = "java"

# substring to be replaced
subString = "tutorialspoint"

# compilation step to escape the word for all cases

# the re.IGNORECASE is used to ignore cases
compileObj = re.compile(re.escape(subString), re.IGNORECASE)

#Substitute the substring with replacing a string using the regex sub() function
resultantStr = compileObj.sub(replaceString, inputString)

# printing resultant string after replacing
print("Resultant string after replacing: ", resultantStr)

Output

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

Input String: hello TuTorialsPOint python
Resultant string after replacing: hello java python

Method 2: Using re.sub(), lambda, re.escape() functions

lambda function

A lambda function is a small anonymous function.

A lambda function can have an unlimited/any number of arguments but only one expression.

Syntax

lambda arguments : expression

Example

The following program returns a string after case-insensitive string replacement using re.sub(), lambda, re.escape() functions -

# importing re(regex) module
import re

# input string
inputString = "hello TuTorialsPOint python"

# printing input string
print("Input String: ", inputString)

# input replace string to be replaced with
replaceString = "java"

# substring to be replaced
subString = "tutorialspoint"
resultantStr = re.sub('(?i)'+re.escape(subString), lambda k: replaceString, inputString)
print("Resultant string after replacing: ", resultantStr)

Output

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

Input String: hello TuTorialsPOint python
Resultant string after replacing: hello java python

Method 3: Using split(), lower() & replace() functions

split() ? splits a string into a list. We can define the separator; the default separator is any whitespace.

lower() ? converts all uppercase characters in a string to lowercase characters

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)

Example

The following program returns a string after case-insensitive string replacement using split(), lower() & replace() functions -

# input string
inputString = "hello TuTorialsPOint python"

# printing input string
print("Input String: ", inputString)

# input replace string to be replaced with
replaceString = "java"

# substring to be replaced
subString = "tutorialspoint"

# splitting input string into a list of words
wordsList = inputString.split()

# traversing through each word of words list
for word in wordsList:

   # checking whether the current word is equal to the given substring

   # by converting them into lowercase using the lower() function
   if(word.lower() == subString.lower()):

      # replacing current word with the input replace string
      inputString = inputString.replace(word, replaceString)
print("Resultant string after replacing: ", inputString)

Output

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

Input String: hello TuTorialsPOint python
Resultant string after replacing: hello java python

Method 4: Using split(), list() and join() functions

join() ? join() is a string function in Python that is used to join elements of a sequence that are separated by a string separator. This function connects sequence elements to convert to a string.

list() function(converts the sequence/iterable to a list).

Example

The following program returns a string after case-insensitive string replacement using split(), list(), and join() functions -

# input string
inputString = "hello TuTorialsPOint python"

# printing input string
print("Input String: ", inputString)

# input replace string to be replaced with
replaceString = "java"

# substring to be replaced
subString = "tutorialspoint"

# splitting input string into a list of words
wordsList = inputString.split()

# traversing through index and word of @@ words list
for index, word in enumerate(wordsList):

   # converting current word into lowercase and checking

   # whether it is equal to substring
   if word.lower() == subString:

      # replacing that word with the given replace string
      wordsList[index] = replaceString

# converting words of wordlist into a string
resultantStr = " ".join([word for word in wordsList])
print("Resultant string after replacing: ", resultantStr)

Output

Input String: hello TuTorialsPOint python
Resultant string after replacing: hello java python

Conclusion

In this article, we learned how to use 4 different methods to case-insensitively replace the given string. Additionally, we learned how to use the regex module's IGNORECASE attribute to ignore the string's cases.