Adding these special characters to our regular expression allow us to do sophisticated matching and extraction while writing very little code.įor example, the caret character is used in regular expressions to match “the beginning” of a line. The power of the regular expressions comes when we add special characters to the search string that allow us to more precisely control which lines match the string. This program does not use the real power of regular expressions, since we could have just as easily used line.find() to accomplish the same result. We open the file, loop through each line, and use the regular expression search() to only print out lines that contain the string “From:”. The following program demonstrates a trivial use of the search function. The simplest use of the regular expression library is the search() function.
The regular expression library re must be imported into your program before you can use it. For more detail on regular expressions, see: In this chapter, we will only cover the basics of regular expressions. As a matter of fact, entire books have been written on the topic of regular expressions. Regular expressions are almost their own little programming language for searching and parsing strings. The reason we have not introduced regular expressions earlier in the book is because while they are very powerful, they are a little complicated and their syntax takes some getting used to. This task of searching and extracting is so common that Python has a very powerful library called regular expressions that handles many of these tasks quite elegantly. Using string methods like split and find and using lists and string slicing to extract portions of the lines. So far we have been reading through files, looking for patterns and extracting various bits of lines that we find interesting.
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