Outline for November 2, 2023

Reading: §14
Due: Homework 3, due November 9, 2023

1. Example: memos
   1. Remember how slowly the recursive Fibonacci number program rfib.py ran? Here is a faster recursive version that uses memos [rfibmemo.py]

2. Recursion: permutations of characters in a string [perm.py]

3. Pattern matching
   1. Regular expressions
   2. Atoms: letters, digits
   3. Match any character except newline: .
   4. Match any of a set of characters: [0123456789], [^0123456789], [0-9]
   5. Repetition: *, +, {m,n}; greedy matching; put ? after and they match as few characters as possible
   6. Match start, end of string: ^, $; $ matches end of line, also
   7. Grouping: (, )
   8. Escape metacharacters: \

4. Useful functions/methods [recomp.py, renocomp.py, regroup.py]
   1. re.compile(str) compiles the pattern into pc (that is, pc = re.compile(str))
   2. pc.match(str) returns None if compiled pattern pc does not match beginning of string str
   3. pc.search(str) returns None if pattern pc does not match any part of string str
   4. pc.findall(str) returns a list of substrings of the stringstr that match the pattern pc
   5. pc.group(str) returns the substring of the string str that the pattern pc matches
   6. pc.start(str) returns the starting position of the match
   7. pc.end(str) returns the ending position of the match
   8. pc.span(str) returns tuple (start, end) positions of match

Matt Bishop Office: 2209 Watershed Sciences Phone: +1 (530) 752-8060 Email: [email protected]

ECS 235A, Computer and Information Security Version of November 1, 2023 at 10:02PM

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