Python all characters except

Python: Remove all non-alphanumeric characters from string

We can use this to all non alphanumeric characters from a string. For this we need to pass a regex pattern that matches all characters except alphanumeric characters like r”[^A-Za-z0-9]+”. Also, as a replacement string we need to pass the empty string. For example,

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sample_str = "Test & [88]%%$$$#$%-+ String 90$" # Remove characters that are not letter or numbers pattern = r'[^A-Za-z0-9]+' sample_str = re.sub(pattern, '', sample_str) print(sample_str)

Here, the sub() function searched for all the non-alphanumeric characters and then replaced them with the empty string. Then finally returned a copy of original string but with only alphanumeric characters. We assigned back this new string back to original variable, it gave an effect that we have delete all non-alphanumeric characters from the string.

Remove all non alphanumeric characters using join() is & isalpha()

In Python, string also provides a function isalpha(). Which returns True if all the characters in calling string object are alphanumeric. We can use this function along with the join() function. So, to remove all non alphanumeric characters from a string, we will iterate over all characters of string one by one and skip the non-alphanumeric characters. Then using the join() function, we will combine the remaining characters. For example,

sample_str = "Test & [88]%%$$$#$%-+ String 90$" # Remove all non alpha-numeric characters from a string sample_str = ''.join(item for item in sample_str if item.isalnum()) print(sample_str)

It deleted all non-alphanumeric characters from string.

Remove all non alphanumeric characters using filter(), join() and isalpha()

We can use the filter() function to filter all non-alphanumeric characters from a string. Steps are as follows,

1. Pass the isalpha() function as the conditional argument to filter() function, along with the string to be modified.
2. filter() function yields only those characters from given string for which isalpha() returns True i.e. only alphanumeric characters.
3. Use join() function to combine all those characters which are yielded by the filter() function i.a. only alphanumeric characters.
4. Assign back the string returned by join() function to original variable. It will give an effect the we have deleted all non alphanumeric characters.

sample_str = "Test & [88]%%$$$#$%-+ String 90$" # Filter only alpha-numeric characters from a string sample_str = ''.join(filter(str.isalnum, sample_str)) print(sample_str)

It deleted all non-alphanumeric characters from string.

Remove all non alphanumeric characters from string using for loop

Create a new empty temporary string. Then iterate over all characters in string using a for loop and for each character check if it is alphanumeric or not. If it is alphanumeric, then append it to temporary string created earlier. When the for loop ends, the temporary string contains only the alphanumeric characters from original string. Assign temporary string to original variable. It will give an effect the we have deleted all non alphanumeric characters. For example,

sample_str = "Test & [88]%%$$$#$%-+ String 90$" # Iterate over all characters in string using a for loop # and select only those characters, which are alpha-numberic mod_string = "" for elem in sample_str: if elem.isalnum(): mod_string += elem sample_str = mod_string print(sample_str)

It deleted all non-alphanumeric characters from string.

Remove all non alphanumeric characters from string except space

We will use the logic explained in above example i.e. iterate over all characters of string using for loop. Pick only alphanumeric characters and space. For example,

sample_str = "Test & [88]%%$$$#$%-+ String 90$" # Iterate over all characters in string using a for loop # and select only those characters, which are alpha-numberic or space mod_string = "" for elem in sample_str: if elem.isalnum() or elem == ' ': mod_string += elem sample_str = mod_string print(sample_str)

It deleted all non-alphanumeric characters from string except space.

We learned about different ways to delete all non-alphanumeric characters from a string in python.

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Remove specific characters from the string

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 s1=re.sub("[$|@|&]","",s) print (s1) # Результат: Hello Python3
 
 
Template to replace → * “[$ | @ | &] ”*
 
 
 
[] * is used to define a set
 
 
 
$ | @ | & * → will search for $ or @ or &
 
 
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
 
Before us is a generator object containing all the letters from the string: 
 s1=””.join(c for c in s if c.isalpha()) 
 
With 'filter ()'
 
s = "Hello$@ Python3&" f = filter(str.isalpha, s) s1 = "".join(f) print(s1)
 
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.
 
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.)
 
 
Remove all characters except letters and numbers
 
With 'isalnum ()'
 
 
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()) print(s1) # Результат: HelloPython3
 
With 're.sub ()'
 
s = "Hello$@ Python3&_" import re s1 = re.sub("[^A-Za-z0-9]", "", s) print(s1) # Результат: HelloPython3
 
Consider * s1 = re.sub (“[^ A-Za-z0–9]”, ””, s) *
 
Remove all numbers from a string using regular expressions
 
With 're.sub ()'
 
 
s = "Hello347 Python3$" import re s1 = re.sub("7", "", s) print(s1) # Результат: Hello Python$
 
Consider * s1 = re.sub (“[0–9]”, ””, s) *
 
 
 
 
5 * - 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 ()'
 
 
s = "1-2$3%4 5a" s1 = "".join(c for c in s if c.isdecimal()) print(s1) # 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) print(s1) # 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) print(s1) # 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.
 
Note
 
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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