See re.sub, for performance consider a re.compile to optimize the pattern once.
Below you find a short version which matches all characters not in the range from A to Z and replaces them with the empty string. The re.I flag ignores the case, thus also lowercase [a-z] characters are replaced.
import re
def charFilter[myString]
return re.sub['[^A-Z]+', '', myString, 0, re.I]
If you really need that loop there are many awnsers, explaining that specifically. However you might want to give a reason why you need a loop.
If you want to operate on the number sequences and thats the reason for the loop consider replacing the replacement string parameter with a function like:
import re
def numberPrinter[matchString] {
print[matchString]
return ''
}
def charFilter[myString]
return re.sub['[^A-Z]+', '', myString, 0, re.I]
In this tutorial, we will look at how to keep only letters [extract alphabets] from a string in Python with the help of examples.
How to extract only alphabets from a string in Python?
You can use a regular expression to extract only letters [alphabets] from a string in Python. You can also iterate over the characters in a string and using the string isalpha[] function to keep only letters in a string.
Let’s look at both the methods with the help of examples –
Extract alphabets from a string using regex
You can use the regular expression 'r[^a-zA-Z]' to match with non-alphabet characters in the string and replace them with an empty string using the re.sub[] function. The resulting string will contain only letters.
Let’s look at an example.
import re # string with letters, numbers, and special characters s = "[email protected]" # keep only letters res = re.sub[r'[^a-zA-Z]', '', s] print[res]
Output:
BuckyBarnes
You can see that the resulting string contains only letters.
Using string isalpha[] function
Alternatively, you can use the string isalpha[] function to remove non-alphabet characters from the string. Use the following steps –
- Create an empty string to store our result string with only letters.
- Iterate through each character in our given string.
- For each character, check if its an alphabet using the string
isalpha[]function. If it is, then add the character to our result string.
Let’s look at an example.
# string with letters, numbers, and special characters
s = "[email protected]"
# keep only letters
res = ""
for ch in s:
if ch.isalpha[]:
res += ch
print[res]Output:
BuckyBarnes
The result string contains only letters from the original string.
The above code can be reduced to fewer lines using list comprehension.
# string with letters, numbers, and special characters s = "[email protected]" # keep only letters res = "".join[[ch for ch in s if ch.isalpha[]]] print[res]
Output:
BuckyBarnes
We get the same result as above.
You might also be interested in –
- Python – Check If String Contains Only Letters
- Python – Remove Non Alphanumeric Characters from String
- Remove Substring From a String in Python
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Piyush is a data scientist passionate about using data to understand things better and make informed decisions. In the past, he's worked as a Data Scientist for ZS and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.
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Sometimes, while working with Python lists, we can have a problem in which we need to extract only those strings which contains only alphabets and discard those which include digits. This has application in day-day programming and web development domain. Lets discuss certain ways in which this task can be performed. Method #1 : Using isalpha[] + list comprehension The combination of above functions can be used to perform this task. In this, we extract the string which are alphabets only using isalpha[] and compile whole logic using list comprehension.
Python3
test_list =
['gfg', 'is23', 'best', 'for2', 'geeks']
print["The original list is : " + str[test_list]]
res = [sub for sub in test_list if sub.isalpha[]]
print["Strings after filtering : " + str[res]]
Output :
The original list is : ['gfg', 'is23', 'best', 'for2', 'geeks'] Strings after filtering : ['gfg', 'best', 'geeks']
Method #2 : Using filter[] + lambda The combination of above methods can be used to perform this task. In this, we perform filtering using filter[] and logic for extension to all strings is done using lambda.
Python3
test_list = ['gfg', 'is23', 'best', 'for2', 'geeks']
print["The original list is : " + str[test_list]]
res = list[filter[lambda sub: sub.isalpha[], test_list]]
print["Strings after filtering : " + str[res]]
Output :
The original list is : ['gfg', 'is23', 'best', 'for2', 'geeks'] Strings after filtering : ['gfg', 'best', 'geeks']
The Time and Space Complexity for all the methods are the same:
Time Complexity: O[n]
Auxiliary Space: O[n]