Here are some exercises for you to try on your own. Solutions are available at http://pragprog.com/titles/gwpy3/practical-programming.
Write a program that makes a backup of a file. Your program should prompt the user for the name of the file to copy and then write a new file with the same contents but with .bak as the file extension.
Suppose the file alkaline_metals.txt contains the name, atomic number, and atomic weight of the alkaline earth metals:
| | beryllium 4 9.012 |
| | magnesium 12 24.305 |
| | calcium 20 20.078 |
| | strontium 38 87.62 |
| | barium 56 137.327 |
| | radium 88 226 |
Write a for loop to read the contents of alkaline_metals.txt and store it in a list of lists, with each inner list containing the name, atomic number, and atomic weight for an element. (Hint: Use string.split.)
All of the file-reading functions we have seen in this chapter read forward through the file from the first character or line to the last. How could you write a function that would read backward through a file?
In Processing Whitespace-Delimited Data, we used the “For Line in File” technique to process data line by line, breaking it into pieces using string method split. Rewrite function process_file to skip the header as normal but then use the Read technique to read all the data at once.
Modify the file reader in read_smallest_skip.py of Skipping the Header so that it can handle files with no data after the header.
Modify the file reader in read_smallest_skip.py of Skipping the Header, so that it uses a continue inside the loop instead of an if. Which form do you find easier to read?
Modify the PDB file reader of Multiline Records, so that it ignores blank lines and comment lines in PDB files. A blank line is one that contains only space and tab characters (that is, one that looks empty when viewed). A comment is any line beginning with the keyword CMNT.
Modify the PDB file reader to check that the serial numbers on atoms start at 1 and increase by 1. What should the modified function do if it finds a file that doesn’t obey this rule?
If you’re still not clear on how directory paths work, try looking at this discussion on Wikipedia: http://en.wikipedia.org/wiki/Path_(computing).