Why does the regex '\d ' match IP addresses like '78.46.92.168:8000' instead of only numeric digits?

Checking Whole String with a Regex

When attempting to determine if a string is numerical using the regex "d ", it can be discovered that the pattern also matches IP addresses like "78.46.92.168:8000." This can be confusing, as one might expect that "d" only matches numeric digits. To understand why this occurs, it's necessary to understand the behavior of "d ".

Understanding "d "

The "d" character class matches any single digit character within the ASCII range (0-9). The " " quantifier denotes one or more occurrences of the preceding element ("d" in this case), indicating that "d " will match a sequence of one or more digits.

In the example string "78.46.92.168:8000," the sequence "78" is a valid match for "d ." It matches the first 78, not the entire string. Since the match succeeds, the code proceeds to call doStuff().

Matching the Whole String

To match the entire string and ensure it only contains numeric digits, it's necessary to use a more specific regex pattern.

• **Adding "^" and "$":** Adding "^" (beginning of string) and "$" (end of string) to the regex ensures that it matches the entire input string. For example, "^d $" would only match strings consisting exclusively of digits.
• Using "isdigit()": Python provides the "isdigit()" method on strings, which returns a boolean value indicating whether the entire string contains only numerical digits. For example, "78.46.92.168:8000".isdigit() would return False because the string contains non-digit characters.

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