Problem 8
Write a program that replaces each line of a file with its reverse. For example, if you run python reverse.py hello.py then the contents of hello.py are changed to \- margorp nohtyp tsrif y )"Idiroin , o11et"(tnirp Of course, if you run Reverse twice on the same file, you get back the original file.
Problem 8
What can your program do with the exception object that an except clause receives?
Problem 9
What is the difference between sequential access and random access?
Problem 9
Write a program that reads cach line in a file, reverses its lines, and writes them to another file. For example, if the file input. txt contains the lines Nary had a liftle lanb Its fleece was white as snow And everyuhere that Mary went The lanb was sure to go. and you run reverse input, txt output, txt then output, txt contains The lanb was sure to go. And everyuhere that Mary went Its fleece was white as snow Mary had a little lanb.
Problem 10
What is the difference between a text file and a binary file?
Problem 13
Write a program that asks the user to input a set of floating-point values. When the user enters a value that is not a number, give the user a second chance to enter the value. After two chances, quit reading input. Add all correctly specificd values and print the sum when the user is done entering data. Use exception handling to detect improper inputs.
Problem 13
Give an output statement to write a date and time in ISO 8601 format, such as 2011-03-01 09:35 Assume that the date and time are given in five integer variables named year, nonth, day, hour, minute.
Problem 16
In order to read a web page (Special Topic 7.4), you need to know its character cncoding (Special Topic 7.3). Write a program that has the URL of a web page as a command-line argument and that fetches the page contents in the proper encoding. Determine the encoding as follows: 1\. After calling urlopen, call input.headers ["content-type"]. You may get a string such as "text/htn1; charset-windows-1251". If so, use the value of the charset attribute as the cncoding. 2\. Read the first line using the "latin 1 " encoding. If the first two bytes of the file are 254255 or 255254 , the encoding is "ut \(f-16^{\prime \prime}\). If the first three bytes of the file are 239187191 , the encoding is "ut \(f-8^{*}\). 3\. Continue reading the page using the "latin 1 " encoding and look for a string of the form encoding=... or charset \(=\ldots\) If you found a match, extract the character encoding (discarding any surrounding quotation marks) and re-read the document with that encoding. If none of these applies, write an error message that the encoding could not be determined.
Problem 16
What is the purposc of the fina11y clause used with a try/except block? Give an example of how it can be used.
Problem 17
Programming Tip \(7.2\) suggests that you use a try/except statement to handle exceptions and a separate try/finally statement to close a file. What would happen if you combined the rwo into a single statement, as below, and the open function raised an exception? try : outfile = open(filenare, "w") Write outpot. except IOError: Hande exoeptiom. fina17y : outfile.closeO You could overcome this problem by moving the call to open outside the try block. What problem do you then have?
