Think Python - Denison University

14.11. Glossary 14314.11 Glossarypersistent: Pertaining to a program that runs indefinitely and keeps at least some of its data inpermanent storage.format operator: An operator, %, that takes a format string and a tuple and generates a string thatincludes theelements of thetuple formattedas specified by theformat string.format string: A string,used withtheformat operator, that contains format sequences.format sequence: A sequence of characters in a format string, like %d, that specifies how a valueshould be formatted.text file: A sequence of characters storedinpermanent storagelikeaharddrive.directory: A named collection of files, alsocalled afolder.path: A stringthat identifies a file.relative path: A path that startsfromthe current directory.absolute path: A path that startsfromthe topmost directory inthefile system.catch: Toprevent anexception fromterminatingaprogram usingthetryandexceptstatements.database: Afilewhosecontentsareorganizedlikeadictionarywithkeysthatcorrespondtovalues.14.12 ExercisesExercise 14.5 The urllib module provides methods for manipulating URLs and downloadinginformation from the web. The following example downloads and prints a secret message fromthinkpython.com:import urllibconn = urllib.urlopen('http://thinkpython.com/secret.html')for line in conn.fp:print line.strip()Run thiscode and follow the instructions you seethere.Exercise14.6 InalargecollectionofMP3files,theremaybemorethanonecopyofthesamesong,stored in different directories or with different file names. The goal of this exercise is to search forthese duplicates.1. Writeaprogramthatsearchesadirectoryandallofitssubdirectories,recursively,andreturnsa list of complete paths for all files with a given suffix (like .mp3). Hint: os.path providesseveral useful functions formanipulating file and path names.2. To recognize duplicates, you can use a hash function that reads the file and generates ashort summary of the contents. For example, MD5 (Message-Digest algorithm 5) takes anarbitrarily-long “message” and returns a 128-bit “checksum.” The probability is very smallthat twofiles withdifferent contents willreturnthe samechecksum.You can read about MD5 at wikipedia.org/wiki/Md5. On a Unix system you can use theprogrammd5sumand apipe tocompute checksums from Python.