| This chapter is full of programs we encourage you to type in and play with. However, here are a few more challenging exercises: See Section B.8.1 for the solutions. Avoiding regular expressions. Write a program that obeys the same requirements as pepper.py but doesn't use regular expressions to do the job. This is somewhat difficult, but a useful exercise in building program logic. Wrapping a text file with a class. Write a class that takes a filename and reads the data in the corresponding file as text. Make it so that this class has three attributes: paragraph, line, word, each of which take an integer argument, so that if mywrapper is an instance of this class, printing mywrapper.paragraph(0) prints the first paragraph of the file, mywrapper.line(-2) prints the next-to-last line in the file, and mywrapper.word(3) prints the fourth word in the file. Describing a directory. Write a function that takes a directory name and describes the contents of the directory, recursively (in other words, for each file, print the name and size, and proceed down any eventual directories). Modifying the prompt. Modify your interpreter so that the prompt is, instead of the >>> string, a string describing the current directory and the count of the number of lines entered in the current Python session. Two hints: the prompt variables (e.g., sys.ps1) doesn't have to be a string but can be any object; printing an instance can have side effects, and is done by calling the instance's __repr__ method. Writing a shell. Using the Cmd class in the cmd module and the functions described in this chapter for manipulating files and directories, write a little shell that accepts the standard Unix commands (or DOS commands): ls (dir) for listing the current directory, cd for changing directory, mv (or ren) for moving/renaming a file, and cp (copy) for copying a file. Redirecting stdout. Modify the mygrep.py script to output to the last file specified on the command line instead of to the console.
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