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Python Regular Expressions in Python Introduction to Regular Expressions Groups

JS Park
JS Park
15,959 Points
Posted by JS Park
JS Park
15,959 Points

What's the point of adding ^ and $?

I don't understand why we add ^ and $ to mark the beginning and end of the string? Aren't we just searching through the entire string? What advantage does breaking the entire string into multiple strings have?

Thanks!

1 Answer

Steven Parker
Steven Parker
230,274 Points
Steven Parker
Steven Parker
230,274 Points

Those characters anchor the pattern to the beginning and end of the string. Otherwise, a match might be made using only a portion of the string when we want it to encompass the entire thing.

Of course, there are times when you specifically want to find a substring or word fragment, and in those cases these symbols would not be part of the expression.

Breaking the pattern into groups allows you to identify separate parts, as shown near the end of the video.

Timothy Tseng
Timothy Tseng
3,292 Points

Hi Steven,

I know it's been awhile since you answered but do you think (or anyone else) can elaborate further?

In this video's case we're "anchoring" the name to the beginning of our group and twitter to the end , right? The ^$ used in this video's case is to help separate? I don't really understand what you mean by "anchor the pattern to the beginning and end of the string"... by string do you mean the string we're searching? Or the string that gets returned by re.findall()

Steven Parker
Steven Parker
230,274 Points
Steven Parker
Steven Parker
230,274 Points

The "anchoring" symbols mean that the string (pattern) you are searching for must begin, end, or both in the string you are searching in. For example, /best/ would be found in "the best way", but /^best/ would not since it does not occur at the start of the string.