Python: Check that a string contains only a certain set of characters

Last update on April 23 2025 12:54:27 (UTC/GMT +8 hours)

1. Allowed Characters Check

Write a Python program to check that a string contains only a certain set of characters (in this case a-z, A-Z and 0-9).

Sample Solution:

Python Code:

import re
def is_allowed_specific_char(string):
    charRe = re.compile(r'[^a-zA-Z0-9]')
    string = charRe.search(string)
    return not bool(string)

print(is_allowed_specific_char("ABCDEFabcdef123450")) 
print(is_allowed_specific_char("*&%@#!}{"))

Sample Output:

True                                                                                                          
False 

Pictorial Presentation:

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to validate that a string contains only lowercase letters and digits.
• Write a Python program to check if a string consists solely of alphanumeric characters and underscores.
• Write a Python program to verify that a string contains only the characters a–z, A–Z, 0–9, and no special symbols.
• Write a Python program to determine if a string matches a regex pattern that allows only letters and numbers, then count the frequency of each character.

Go to:

• Python Regular Expression Exercises Home ↩
• Python Exercises Home ↩

Previous: Python Regular Expression Home.
Next: Write a Python program that matches a string that has an a followed by zero or more b's.

Python Code Editor:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.