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An Introduction to Python – Part IV

An Introduction to Python – Part IV. Dr. Nancy Warter-Perez June 23, 2005. Overview. Creating 2-D Lists (already covered) Scopes Modules Doc Strings Debugging Project Development Time. To create a 2-D list L, with C columns and R rows initialized to 0: L = [[]] #empty 2-Dlist

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An Introduction to Python – Part IV

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  1. An Introduction to Python – Part IV Dr. Nancy Warter-Perez June 23, 2005

  2. Overview • Creating 2-D Lists (already covered) • Scopes • Modules • Doc Strings • Debugging • Project Development Time Introduction to Python – Part IV

  3. To create a 2-D list L, with C columns and R rows initialized to 0: L = [[]] #empty 2-Dlist L = [[0 for col in range(C)] for row in range(R)] To assign the value 5 to the element at the 2nd row and 3rd column of L L[2][3] = 5 Creating 2-D Lists Introduction to Python – Part IV

  4. Scopes • Scopes divine the “visibility” of a variable • Variables defined outside of a function are visible to all of the functions within a module (file) • Variables defined within a function are local to that function • To make a variable that is defined within a function global, use the global keyword Ex 2: x = 5 def fnc(): global x x = 2 print x, fnc() print x >>> 2 2 Ex 1: x = 5 def fnc(): x = 2 print x, fnc() print x >>> 2 5 Introduction to Python – Part IV

  5. Modules • Why use? • Code reuse • System namespace partitioning (avoid name clashes) • Implementing shared services or data • How to structure a Program • One top-level file • Main control flow of program • Zero or more supplemental files known as modules • Libraries of tools Introduction to Python – Part IV

  6. Modules - Import • Import – used to gain access to tools in modules Ex: contents of file b.py def spam(text): print text, 'spam' contents of file a.py import b b.spam('gumby') Introduction to Python – Part IV

  7. #comments In-file documentation The dir function Lists of attributes available on objects Docstrings:__doc__ In-file documentation attached to objects Python Documentation Sources Introduction to Python – Part IV

  8. Dir and DocString Example Ex: b.py # Internal comment """Module Docstring comment """ def fn(): """Function Docstring comment """ >>> import b >>> dir(b) ['__builtins__', '__doc__', '__file__', '__name__', 'fn'] >>> print b.__doc__ Module Docstring comment >>> print b.fn.__doc__ Function Doctring comment Introduction to Python – Part IV

  9. Debugging • Two types of bugs • Syntax errors – “easy” to find • Logical errors – harder to find • Can be a problem in your algorithm • Can be a problem in your coding • Debugging a program is like solving a puzzle • Must first understand what your program is supposed to do • Logically trace what is happening in your program • What do you expect to happen versus what happened • Follow the flow of data • Follow the flow of control Introduction to Python – Part IV

  10. Debugging Tools/Methods • Can use print statements to “manually” debug • Can use debugger in PythonWin • In Class Example Introduction to Python – Part IV

  11. Workshop • Separate your LCS functions into a different module • Import the module and call the functions from within your while loop (continually prompting the user if they want to continue) • Trace through your program • Use print statements to view the score and trace back matrices as they are formed • Using the debugger to view the score and trace back matrices Introduction to Python – Part IV

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