---Oct. 5, 2020, 8:11 a.m.

5 Ways to Remove Unnecessary Characters from a String in Python

Remove specific characters from the string

Let's use ' str.replace '

With the help of * str.replace *, we can change some characters to others. If we just want to remove some characters, then we simply replace them with an empty string. * str.replace () * will apply the replacement to all matches found.

s="Hello$ Python3$"
s1=s.replace("$", "")
print (s1)
# Результат: Hello Python3

If we can specify a limit for the number of matches, so as not to remove all characters.

s="Hello$ Python3$"
s1=s.replace("$", "", 1)
print (s1)
# Результат: Hello Python3$

With ' re.sub '

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

> Returns the string obtained by replacing the leftmost non-overlapping
> matches a pattern in a string to the value repl. If pattern matches
> not found, an unmodified string is returned
> - From Python documentation

If we want to remove characters, then we simply replace the matches with an empty string.

s="Hello$@& Python3$"
import re
print (s1)
# Результат: Hello Python3


  • Template to replace → * “[$ | @ | &] ”*
    • [] * is used to define a set
    • $ | @ | & * → will search for $ or @ or &
  • Replace with an empty string
  • If the above characters are replaced found, then they are replaced with an empty string

Remove all characters except letters

With 'isalpha ()'

  • isalpha () * is used to check if a string contains only letters. Returns * True * if it is a letter. We will go through each character in the string and check if it is a letter.


s="Hello$@ Python3&"
s1="".join(c for c in s if c.isalpha())
print (s1) 
# Результат: HelloPython

s=”Hello$@ Python3&”

(c for c in s if c.isalpha())

Result → * ['H', 'e', 'l', 'l', 'o', 'P', 'y', 't', 'h', 'o', 'n'] *

Before us is a generator object containing all the letters from the string:
s1=””.join(c for c in s if c.isalpha())

  • ””. Join * will join all characters into one line.

With 'filter ()'

s = "Hello$@ Python3&"
f = filter(str.isalpha, s)
s1 = "".join(f)

f = filter(str.isalpha, s)

The * filter () * function will apply the * str.isalpha * method to each element of the string, and if it gets * true *, then we return the element. Otherwise, skip.

s1 = ””.join(f)

The * filter () * function will return an iterator containing all the letters of the given string, and * join () * will "glue" all the elements together.

With 're.sub ()'

s = "Hello$@ Python3$"
import re
s1 = re.sub("[^A-Za-z]", "", s)
print (s1)
# Результат: HelloPython

Consider * s1 = re.sub (“[^ A-Za-z]”, ””, s) *

    • “[ A-Za-z]” * → Searches for all characters except letters. If you specify * * at the beginning of the set, then all those characters that are NOT specified in the set will match the pattern. (for Russian words use * [^ A-Ya-z] * - ed.)
  • All characters matching the pattern will be replaced with an empty string.
  • All characters except letters will be removed.

Remove all characters except letters and numbers

With 'isalnum ()'

  • isalnum () * is used when we want to define whether a string consists of numbers or letters only.

Let's go through each character in the string to identify the characters we need.

s = "Hello$@ Python3&"
s1 = "".join(c for c in s if c.isalnum())
# Результат: HelloPython3

With 're.sub ()'

s = "Hello$@ Python3&_"
import re
s1 = re.sub("[^A-Za-z0-9]", "", s)
# Результат: HelloPython3

Consider * s1 = re.sub (“[^ A-Za-z0–9]”, ””, s) *

    • “[^ A-Za-z0-9]” * → This pattern will search for all characters except letters and numbers.
  • All found characters will be replaced with an empty string
  • All symbols except letters and numbers are removed.

Remove all numbers from a string using regular expressions

With 're.sub ()'

s = "Hello347 Python3$"
import re
s1 = re.sub("[0-9]", "", s)
# Результат: Hello Python$

Consider * s1 = re.sub (“[0–9]”, ””, s) *

    • [0-9] * - numbers from 0 to 9
    • re.sub (“[0–9]”, ””, s) * - if there are matches, replace with an empty string

Remove all characters from the string except numbers

With 'isdecimal ()'

  • isdecimal () * returns true if all characters in the string are numbers, false otherwise.

s = "1-2$3%4 5a"
s1 = "".join(c for c in s if  c.isdecimal())
# Результат: 12345

We go over each character of the string and check whether it is a digit. * "". join () * joins all elements.

With 're.sub ()'

s = "1-2$3%4 5a"
import re
s1 = re.sub("[^0-9]", "", s)
# Результат: 12345

Consider * s1 = re.sub (“[^ 0–9]”, ””, s) *

    • [^ 0-9] * will search for all characters except 0 through 9
    • re.sub (“[^ 0-9]”, ””, s) * all characters except numbers will be replaced with an empty string.

With 'filter ()'

s = "1-2$3%4 5a"
f = filter(str.isdecimal, s)
s1 = "".join(f)
# Результат: 12345

Consider * f = filter (str.isdecimal, s) *

The * filter () * function will execute the * str.isdecimal * method for each character, if it returns true, then it adds it to the generator. The generator is then unpacked into a finished string using the * join () * method.


Strings in Python are immutable objects, so all of the above methods remove characters from the given string and return a new one, they do not change the state of the original string.

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Я конечно понимаю, что это статья с Медиума, но всё равно - очень не хватает сравнения скорости выполнения замен.


Опечатка в заголовке статьи - 5 СОпсобов


помогло, спасибо


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