An Introduction to Python Part IV

1
An Introduction to Python Part IV

• Dr. Nancy Warter-Perez
• May 19, 2005

2
Overview

• Scopes
• Modules
• Doc Strings
• Debugging

3
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 gtgtgt 2 2
Ex 1 x 5 def fnc() x 2 print
x, fnc() print x gtgtgt 2 5
4
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

5
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')

6
Python Documentation Sources

• comments In-file documentation
• The dir function Lists of attributes
  available on objects
• Docstrings__doc__ In-file documentation
• attached to objects

7
Dir and DocString Example

• Ex b.py
• Internal comment
• """Module Docstring comment """
• def fn()
• """Function Docstring comment """
• gtgtgt import b
• gtgtgt dir(b)
• '__builtins__', '__doc__', '__file__',
  '__name__', 'fn'
• gtgtgt print b.__doc__
• Module Docstring comment
• gtgtgt print b.fn.__doc__
• Function Doctring comment

8
Debugging

• Can use print statements to manually debug
• Can use debugger in PythonWin
• In Class Example

9
Project Teams and Presentation Assignments

• Base Project (Global Alignment)
• Extension 1 (Local Alignment)
• Extension 2 (Ends-Free Global Alignment)
• Extension 3 (Affine Gap Penalty)
• Extension 4 (Database)