Python isalnum: String Is Alphanumeric

Use the isalnum method to see whether a string contains only letters and digits.

Isalnum. Sometimes we want to ensure a string contains not punctuation or other whitespace. We want to see if the string contains just letters and digits.

With isalnum, we have a method that loops over the characters in the string. If any whitespace, punctuation, or other weird characters are found, it returns false.

An example. Here we see a program that uses isalnum. We can call isalnum() on a string instance, or use str.isanum and pass the string as the argument.

Tests: We have 7 strings in our tests list. Some have spaces, punctuation, and one is an empty string.


Result: The only strings that cause isalnum to return true are the ones with no whitespace or punctuation (and at least 1 character).

Python program that uses isalnum method tests = [] tests.append("Dot Net Perls") tests.append("DotNetPerls") tests.append("Dot_Net_Perls") tests.append("Dot0123") tests.append("dotnetperls") tests.append("123") tests.append("") for test in tests: # Test each string for alphanumeric status with isalnum. if test.isalnum(): print("isalnum: [", test, "]") else: print("false: [", test, "]") Output false: [ Dot Net Perls ] isalnum: [ DotNetPerls ] false: [ Dot_Net_Perls ] isalnum: [ Dot0123 ] isalnum: [ dotnetperls ] isalnum: [ 123 ] false: [ ]

A useful method. Often we want to validate strings before putting them into a dictionary or list. Isalnum is a good method to remember—it is easier than trying to write a similar method.DictionaryList

A review. When possible, methods like isalnum() from the standard library should be reused. They do not need testing—they are convenient and easy to understand.
Dot Net Perls
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