How do you select only alpha characters in python?

1. Use the isalnum() Method to Remove All Non-Alphanumeric Characters in Python String
2. Use the filter() Function to Remove All Non-Alphanumeric Characters in Python String
3. Use Regular Expressions to Remove All Non-Alphanumeric Characters in Python String

Alphanumeric characters contain the blend of the 26 characters of the letter set and the numbers 0 to 9. Non-alphanumeric characters include characters that are not letters or digits, like + and @.

In this tutorial, we will discuss how to remove non-alphanumeric characters from a string in Python.

Use the isalnum() Method to Remove All Non-Alphanumeric Characters in Python String

We can use the isalnum() method to check whether a given character or string is alphanumeric or not. We can compare each character individually from a string, and if it is alphanumeric, then we combine it using the join() function.

For example,

string_value = "alphanumeric@123__"
s = ''.join(ch for ch in string_value if ch.isalnum())
print(s)

Output:

alphanumeric123

Use the filter() Function to Remove All Non-Alphanumeric Characters in Python String

The filter() function is used to construct an iterator from components of the iterable object and filters the object’s elements using a function.

For our problem, the string is our object, and we will use the isalnum() function, which checks whether a given string contains alphanumeric characters or not by checking each character. The join() function combines all the characters to return a string.

For example,

string_value = "alphanumeric@123__"
s = ''.join(filter(str.isalnum, string_value))
print(s)

Output:

alphanumeric123

This method does not work with Python 3.

Use Regular Expressions to Remove All Non-Alphanumeric Characters in Python String

A regular expression is an exceptional grouping of characters that helps you match different strings or sets of strings, utilizing a specific syntax in a pattern. To use regular expressions, we import the re module.

We can use the sub() function from this module to replace all the string that matches a non-alphanumeric character by an empty character.

For example,

import re
string_value = "alphanumeric@123__"
s=re.sub(r'[\W_]+', '', string_value)
print(s)

Output:

alphanumeric123

Alternatively, we can also use the following pattern.

import re
string_value = "alphanumeric@123__"
s = re.sub(r'[^a-zA-Z0-9]', '', string_value)
print(s)

Output:

alphanumeric123

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