Python: Match a string that contains only upper and lowercase letters, numbers, and underscores

Last update on March 31 2025 12:57:30 (UTC/GMT +8 hours)

14. Alphanumeric Underscore Only

Write a Python program to match a string that contains only upper and lowercase letters, numbers, and underscores.

Sample Solution:

Python Code:

import re
def text_match(text):
        patterns = '^[a-zA-Z0-9_]*$'
        if re.search(patterns,  text):
                return 'Found a match!'
        else:
                return('Not matched!')

print(text_match("The quick brown fox jumps over the lazy dog."))
print(text_match("Python_Exercises_1"))

Sample Output:

Not matched!                                                                                                  
Found a match!

Pictorial Presentation:

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to validate that a string contains only letters, digits, and underscores.
• Write a Python script to filter a list of strings, keeping only those that match the pattern of alphanumerics and underscores.
• Write a Python program to check if a string strictly adheres to a regex that permits only upper/lowercase letters, numbers, and underscores.
• Write a Python program to replace any character not a letter, digit, or underscore with an empty string.

Python Code Editor:

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