Unit 6 File processing Special thanks to Roy McElmurry John Kurkowski Scott Shawcroft Ryan Tucker Paul Beck for their work Except where otherwise noted this work is licensed under http creativecommons org licenses by nc sa 3 0 Reading Files name open filename opens the given file for reading and returns a file object name read file s entire contents as a name readline name readlines next line from file as a string file s contents as a list of lines string the lines a file object can also be read using a for from f open hours txt loop f read 123 Susan 12 5 8 1 7 6 3 2 n 456 Brad 4 0 11 6 6 5 2 7 12 n 789 Jenn 8 0 8 0 8 0 8 0 7 5 n 2 File Input Template A template for reading files in Python name open filename for line in name statements input open hours txt for line in input print line strip strip removes n 123 Susan 12 5 8 1 7 6 3 2 456 Brad 4 0 11 6 6 5 2 7 12 789 Jenn 8 0 8 0 8 0 8 0 7 5 3 Exercise Write a function input stats that accepts a file name as a parameter and that reports the longest line in the file example input file carroll txt Beware the Jabberwock my son the jaws that bite the claws that catch Beware the JubJub bird and shun the frumious bandersnatch expected output input stats carroll txt longest line 42 characters the jaws that bite the claws that catch 4 Exercise Solution def input stats filename input open filename longest for line in input if len line len longest longest line print Longest line len longest print longest 5 Recall String Methods Java Python length len str startsWith endsWith startswith endswith toLowerCase toUpperCase upper lower isupper islower capitalize swapcase indexOf find trim strip ord chr name Martin Douglas Stepp name upper MARTIN DOUGLAS STEPP name lower startswith martin True len name 20 6 String Splitting split breaks a string into tokens that you can loop over name split name split delimiter break by whitespace break by delimiter join performs the opposite of a split delimiter join list of tokens name Brave Sir Robin for word in name split print word Brave Sir Robin LL join name split r BLLave SiLL Robin 7 Splitting into Variables If you know the number of tokens you can split them directly into a sequence of variables var1 var2 varN string split may want to convert type of some tokens type value s Jessica 31 647 28 name age money s split name Jessica int age 31 float money 647 28 8 Exercise Suppose we have this hours txt data 123 Suzy 9 5 8 1 7 6 3 1 3 2 456 Brad 7 0 9 6 6 5 4 9 8 8 789 Jenn 8 0 8 0 8 0 8 0 7 5 Compute each worker s total hours and hours day Assume each worker works exactly five days Suzy ID 123 worked 31 4 hours 6 3 day Brad ID 456 worked 36 8 hours 7 36 day Jenn ID 789 worked 39 5 hours 7 9 day 9 Exercise Answer hours py 1 2 3 4 5 6 7 8 9 10 input open hours txt for line in input id name mon tue wed thu fri line split cumulative sum of this employee s hours hours float mon float tue float wed float thu float fri print name ID id worked hours hours hours 5 day 10 Writing Files name open filename w name open filename a opens file for write deletes previous contents or opens file for append new data goes after previous data name write str file writes the given string to the out name close open output txt saves file w once out write Hello world n out write How are you out close writing is done open output txt read Hello world nHow are you 11 Exercise Write code to read a file of gas prices in USA and Belgium 8 20 8 08 8 38 3 81 3 84 3 92 3 21 11 3 28 11 4 4 11 Output the average gas price for each country to an output file named gasout txt 12
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