Comments on week 3 examples:

 A module that uses sys.argv, such as command_line.py from week 3,
can't be usefully run in the IDLE interpreter, since there is no easy way
to provide the command line arguments.

Comments on assignment due week 3, Oct 25: concordance

Problem statement: http://staff.washington.edu/jon/uw_python/fall_2011/assign_3.txt

My solution: http://staff.washington.edu/jon/uw_python/fall_2011/concordance.py

See also points 1 - 3 in comments_2.txt (on week 2 homework).

1.  File objects vs. file names - here "myfile.txt" is file name, fi is file object:

    fi = open("myfile.txt")

Pass the file objects to concordance, not the names - so open is
outside concordance, function, not inside

2.  After file = open(filename) all you need is

 for line in file: 
   ... now line is a string ...

You don't need file.read() in the for loop body
file object is an iterable, it knows how to get the next element, read is implicit

3.  Can use enumerate to get line count automatically, no need to maintain counter 

 for i, line in enumerate(file):
    .. i is line number, line is a string ...

4.  I expected if str in line: ...  , but if re.search(str, line):...  works fine too.
    So does if line.find(str) > -1: ...

5. Don't forget to close the files!  Nothing may appear in output file until close.

6.  In general, unless I ask, don't worry about exceptions (missing
  file, invalid args, ...).  The usual expectation in Python is that
  the function docstring states a "contract" that the caller is
  expected to honor; if not, the function may not work and is not
  obligated to try to recover.  If you want to check args and handle
  exceptions, this is usually done in the caller (script), not in the
  function.  In small scripts, it is usual to just let it crash
  (rather than try ... except ...), crash message is sufficiently
  informative.