Skip to content
Related Articles
Open in App
Not now

Related Articles

Python | Removing unwanted characters from string

Improve Article
Save Article
  • Difficulty Level : Easy
  • Last Updated : 30 Dec, 2022
Improve Article
Save Article

The generic problem faced by the programmers is remove unwanted characters from a string using Python. But sometimes the requirement is way above and demands the removal of more than 1 character, but a list of such malicious characters. These can be in the form of special characters for reconstructing valid passwords and many other applications possible. So our task is to remove the unwanted characters from the string.

Removing symbol from string using str.isalnum()

Python String isalnum() method checks whether all the characters in a given string are alphanumeric or not. It returns a boolean as True – If all the characters are alphanumeric or else false – If one or more characters are not alphanumeric.

Python3




string = "Ge;ek * s:fo ! r;Ge * e*k:s !"
 
test_str = ''.join(letter for letter in string if letter.isalnum())
print(test_str)

Output:

GeeksforGeeks

Removing symbol from string using replace() 

One can use str.replace() inside a loop to check for a bad_char and then replace it with the empty string hence removing it. This is the most basic approach and inefficient on a performance point of view.

Python3




# initializing bad_chars_list
bad_chars = [';', ':', '!', "*", " "]
 
# initializing test string
test_string = "Ge;ek * s:fo ! r;Ge * e*k:s !"
 
# printing original string
print("Original String : " + test_string)
 
# using replace() to
# remove bad_chars
for i in bad_chars:
    test_string = test_string.replace(i, '')
 
# printing resultant string
print("Resultant list is : " + str(test_string))

Output : 

Original String : Ge;ek*s:fo!r;Ge*e*k:s!
Resultant list is : GeeksforGeeks

Removing symbol from string using join() + generator 

By using Python join() we remake the string. In the generator function, we specify the logic to ignore the characters in bad_chars and hence construct a new string free from bad characters.

Python3




# initializing bad_chars_list
bad_chars = [';', ':', '!', "*", " "]
 
# initializing test string
test_string = "Ge;ek * s:fo ! r;Ge * e*k:s !"
 
# printing original string
print("Original String : " + test_string)
 
# using join() + generator to
# remove bad_chars
test_string = ''.join(i for i in test_string if not i in bad_chars)
 
# printing resultant string
print("Resultant list is : " + str(test_string))

Output : 

Original String : Ge;ek*s:fo!r;Ge*e*k:s!
Resultant list is : GeeksforGeeks

Removing symbol from string using translate() 

The most elegant way to perform this particular task, this method is basically used for achieving the solution to this kind of problems itself, we can translate each bad_char to an empty string and get the filtered string.

Python3




import string
# initializing bad_chars_list
bad_chars = [';', ':', '!', "*"]
 
# initializing test string
test_string = "Ge;ek * s:fo ! r;Ge * e*k:s !"
 
# printing original string
print("Original String : " + test_string)
 
# using translate() to
# remove bad_chars
delete_dict = {sp_character: '' for sp_character in string.punctuation}
delete_dict[' '] = ''
table = str.maketrans(delete_dict)
test_string = test_string.translate(table)
 
# printing resultant string
print("Resultant list is : " + str(test_string))

Output : 

Original String : Ge;ek*s:fo!r;Ge*e*k:s!
Resultant list is : GeeksforGeeks

Removing symbol from string using filter() 

This is yet another solution to perform this task. Using the lambda function, filter function can remove all the bad_chars and return the wanted refined string.

Python3




# initializing bad_chars_list
bad_chars = [';', ':', '!', "*"]
 
# initializing test string
test_string = "Ge;ek*s:fo!r;Ge*e*k:s!"
 
# printing original string
print("Original String : " + test_string)
 
# using filter() to
# remove bad_chars
test_string = ''.join((filter(lambda i: i not in bad_chars,
                              test_string)))
# printing resultant string
print("Resultant list is : " + str(test_string))

Output: 

Original String : Ge;ek*s:fo!r;Ge*e*k:s!
Resultant list is : GeeksforGeeks

Removing symbol from string using re.sub() function: 

Regular expressions are used to identify the bad character in the string and re.sub function is used to replace the bad_char from the string. 

Python3




import re
 
# initializing string
test_str = "Ge;ek * s:fo ! r;Ge * e*k:s !"
 
# Bad character list
bad_char = [";", "!", "*", ":", " "]
 
# printing original string
print("The original string is : " + test_str)
 
# using re.sub()
# remove bad_char from string
temp = ''
for i in bad_char:
    temp += i
res = re.sub(rf'[{temp}]', '', test_str)
 
# printing result
print("The strings after extra space removal : " + str(res))

Output: 

The original string is : Ge;ek * s:fo ! r;Ge * e*k:s !
The strings after extra space removal : GeeksforGeeks

Removing symbol from string using in ,not in operators

in and not in operators are used to check the presence of unwanted characters in the string.

Python3




# Python3 code to demonstrate
# removal of bad_chars
 
# initializing bad_chars_list
bad_chars = [';', ':', '!', "*", " "]
 
# initializing test string
test_string = "Ge;ek * s:fo ! r;Ge * e*k:s !"
 
# printing original string
print ("Original String : " + test_string)
 
s=""
for i in test_string:
    if i not in bad_chars:
        s+=i
 
# printing resultant string
print ("Resultant list is : " + str(s))

Output

Original String : Ge;ek * s:fo ! r;Ge * e*k:s !
Resultant list is : GeeksforGeeks

Using a combination of the map function and a lambda function:

One approach that you can use to remove unwanted characters from a string is to use a combination of the map function and a lambda function. The map function applies a function to each element in an iterable, such as a list or string. The lambda function is a small anonymous function that can take in any number of arguments but only has one expression.

Here is an example of how you can use map and a lambda function to remove unwanted characters from a string:

Python3




# Initialize list of unwanted characters
bad_chars = [';', ':', '!', "*", " "]
 
# Initialize test string
test_string = "Ge;ek * s:fo ! r;Ge * e*k:s !"
 
# Print original string
print("Original String : " + test_string)
 
# Use map and lambda function to remove unwanted characters
filtered_string = ''.join(map(lambda x: x if x not in bad_chars else '', test_string))
 
# Print filtered string
print("Filtered String : " + filtered_string)
#This code is contributed by Edula Vinay Kumar Reddy

Output

Original String : Ge;ek * s:fo ! r;Ge * e*k:s !
Filtered String : GeeksforGeeks

The time complexity of the solution using map and lambda is O(n), where n is the length of the list. The solution needs to iterate through the list once to remove the unwanted characters from each string in the list.

The space complexity of the solution is O(n), as a new list is created to store the modified strings. The size of the new list is equal to the size of the input list, so the space complexity is linear.


My Personal Notes arrow_drop_up
Related Articles

Start Your Coding Journey Now!