In computer programming, a string is a sequence of characters. A number is a mathematical object used to represent quantities. To check if a string is a number, we can use the `isdigit()` method of the string object. This method returns True if all characters in the string are digits, and False otherwise.
Checking if a string is a number is important for a variety of reasons. For example, we may want to ensure that a user has entered a valid number into a form field. We may also want to convert a string to a number so that we can perform mathematical operations on it.