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.