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Lecture 1

CS 1110 Lecture 1: November 17 – Re Building

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University of Virginia
Computer Science
CS 1110

November 17 Re Building Sunday, November 5, 2017 11:19 AM Guidelines 1. Create good and bad example stirngs first; mark them off manually 2. Use r'' strings not '' strings 3. Go left to right 4. Pick the right kind of "or": [ab] for single character, (ab|cd) for longer 5. Optional: ()?, And several: ()* [^oe] selects complement of oe, and selects everything but oe Three rules of Regex: 1. Left to right: you want to build leftmost to rightmost o Write down some examples and cross them off as you go 2. Kinds of "one of": doesn't matter which ones come up 3. Maybe, many, one o Question mark signifies maybe x after this >> ( )? Question mark is only good for single character o May be one of them: ? o Might be 0 or more: * o Might be 1 or more: + You should pretty much always use an 'r' string inside a regular expression so backlashes work in a certain way How to handle back\slashes: 16:30 Write single copy of thing to be repeated, and put a parenthesis and * after it " ( [^"\\]*(\\.)? )* " Is the same as " ( [^"\\] | \\.)* " Either non backlash periods or period Strings = re.compile(r' " ( [^"\\] | \\.)* " ') For match in strings.finditer(text): Print( Example: one
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