The isalnum, isalpha and isspace Methods

In my previous articles I covered quite a few string methods. If you haven’t read those articles, feel free to do it. Here they are:

1) formatting methods

2) statistical methods

3) searching methods

4) boolean methods

This article is actually a continuation of the article on string boolean methods. Today we’ll be talking about three methods, which you can use to check whether a given string contains only a specific type of characters, like only letters, digits or white spaces. The methods are isalnum, isalpha and isspace.

Here’s the video version of the article:

The isalnum Method

The method isalnum checks whether the string contains only alphanumeric characters. If so, it returns True. If there is at least one non-alphanumeric character or if the string is empty, it returns False:

>>> text = "abcdef123"
>>> text.isalnum()
True

>>> text = "here are some spaces"
>>> text.isalnum()                  # we also have whitespaces
False

>>> text = "some_characters,()"
>>> text.isalnum()                  # we also have other characters
False

>>> textEmpty = ""
>>> textEmpty.isalnum()             # empty string
False

The isalpha Method

The next method we’ll be talking about is isalpha.

isalpha returns True if the string is not empty and contains only alphabetic characters:

>>> "Please help".isalpha()  # There’s also a space
False

>>> "Help".isalpha()
True

The isspace Method

Finally, let’s talk briefly about the isspace method.

isspace returns True if the string contains only whitespace characters, so spaces, newlines, tabs:

>>> "".isspace()  # no characters at all
False

>>> " ".isspace()
True

>>> "          ".isspace()
True

>>> "  \n".isspace()
True

>>> "  \t\t \n  ".isspace()
True