week_4.txt  Nov 1, 2011
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 Lists, tuples, dictionaries - heart of Python! - next 2 or 3 weeks
  Now it gets interesting - we'll go beyond the books in lectures, reading

 Our story so far
  modules, python command, IDLE
  values (objects), types, expressions, variables,
   statements, print, assignment, for, while, 
   function def and call, import, files, exceptions,
   strings (str type, library, regex, unicode)
   

 But first - some midcourse corrections














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 Midcourse corrections: more time working on / dicussing exercises in class

   lecture 1     - 45 min   6:00 pm
   lab/q&a 1     - 30 min   6:45 
   student talks - 30 min   7:15
   lecture 2     - 45 min   7:45 
   lab/q&a 2     - 30 min   8:30
   dismiss                  9:00 

 Lecture: 2 x 45 min = 90 min

 Student lightning talks: 4 x 5 min + scene changing <= 30 min
 
 Lab + Q&A: 2 x 30 min = 60 min
  
 I will assign an exercise or other activity before labs

 Weekly homework exercise will cover preceding readings, lectures










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Homework assignments - mechanics

 Hand in hardcopy in person on due date - even if not done
  Use email, github etc. only if you can't be here (excused absence)
  Late is better than never, still prefer hardcopy
  I will only return hardcopy (I do record email etc.) 


















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Homework assignments - general guidance

 Follow directions
   I will usually specify function name and arguments - do just that!

 Important distinctions
  function def vs. function call - usually exercise requires both
  library module vs script - usually exercise is library module

 Unless I ask, don't worry about exceptions (missing file, invalid args, ...)
  Function docstring states "contract" that caller is expected to honor
  Usually check args and handle exceptions in caller (script), not function
  In small scripts, just let it crash (rather than try ... except ...)
 











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Homework review

 See posted solutions and comments linked to web page
 
 Week 2: print_grid
  Downey's problem did not require grid size argument
  Downeys solution did not use loop, difficult to generalize
  Small change in requirements can require large change in solution!

 Week 3: concordance
  Pass file objects, not file names, to function
  Open file to get file object before calling function, close after
  Library design: make it as general purpose as possible
  Passing objects means you can also use it on web pages, processes, ...
  File object is an iterator, 'for line in file:' implicitly reads next line










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Homework - this week - most_frequent

 Make histogram, then sort(reverse=True)
  Copy histogram from Downey, returns dictionary
  Get list of tuples from dictionary with d.items()
  Tuples are in wrong order, we want to sort by values, not keys
  Several approaches
   reverse pairs by loop or list comprehension
   OR use key= arg to dictionary with lambda or itemgetter