Python est une lettre ou un numéro Functic

isalnum()
is a built-in Python function that checks 
whether all characters in a string are alphanumeric. 
In other words, isalnum() checks whether a string contains only letters 
or numbers or both.
If all characters are alphanumeric, isalnum() returns the value True ; 
otherwise, the method returns the value False
Xing Wang