Validating Numeric Strings with Regular Expressions

In attempting to validate numeric strings using the regular expression "\d ", you've encountered unexpected matches for IP addresses. To understand why, let's delve into the specifics of regular expression matching.

The "\d" pattern matches any single digit from 0 to 9. "\d " matches any sequence of one or more digits. While this seems straightforward, it's crucial to note that it checks only "within" the string, not from the start to end.

In your example, the string "78.46.92.168:8000" contains a sequence of digits ("78") at the beginning of the string. Hence, "\d " matches this sequence even though the entire string is not numeric due to the presence of "." and ":".

Solution:

To validate strings that are numeric from beginning to end, you can use the following expressions:

1. ^\d $: This pattern anchors the match to the start and end of the string, ensuring it contains only digits.
2. "78.46.92.168:8000".isdigit(): This Pythonic method checks if the entire string contains numeric characters only.