Copyright © 2006 The McGraw-Hill Companies, Inc. Programming Languages 2nd edition Tucker and Noonan Chapter 13 Object-Oriented Programming I am surprised that ancient and Modern writers have not attributed greater importance to the laws of inheritance... Alexis de Tocqueville

Copyright © 2006 The McGraw-Hill Companies, Inc. Contents 13.1 Prelude: Abstract Data Types 13.2 The Object Model 13.3 Smalltalk 13.4 Java 13.5 Python

Copyright © 2006 The McGraw-Hill Companies, Inc Python Multiparadigm –Imperative –Object-orientd –Functional Scripting language Dynamically typed

Copyright © 2006 The McGraw-Hill Companies, Inc. General Characteristics Builtin types: int, float, infinite precision integers, complex numbers, strings,... Data structure –Lists: [1, [2, "allen"], "bob", ] –Hashes: ["Tucker": "Bowdoin", "Noonan": "W&M"] –Tuples: (238111, "allen", "bob") Strings: viewed as list of characters –List operators work on strings

Copyright © 2006 The McGraw-Hill Companies, Inc. Python "less forgiving" than Perl –Cannot do string operations on numbers –Or vice versa –Cannot index past end of list –Must append to end of a list

Copyright © 2006 The McGraw-Hill Companies, Inc. Statements fairly conventional Indentation used for compound statements No $var as in Perl (bareword error) Reference semantics used for assignment Multiple inheritance All methods and instance variables are public. Variables must be set before being referenced. Run time type identification Reflection

Copyright © 2006 The McGraw-Hill Companies, Inc. Examle: Polynomials Represent Polynomials: 3 x 2 + 5x - 7 Representation: #(-7 5 3) Subclass of Magnitude

Copyright © 2006 The McGraw-Hill Companies, Inc. class Polynomial: def __init__(self, coef): """constructor""" self.coefficient = [ ] + coef def degree(self): """Highest power with a non-zero coefficient""" return len(coefficient)

Copyright © 2006 The McGraw-Hill Companies, Inc. def coefficient(self, power): """Coefficient of given power""" if power > len(coefficient): return 0 return coefficient[power] def asList(self): """return copy of coefficient""" return [ ] + coefficient

Copyright © 2006 The McGraw-Hill Companies, Inc. def __eq__(self, aPoly): """return self == aPoly""" return coefficient == aPoly.asList( ) def __ne__(self, aPoly): """return self <> aPoly.asList( )""" return coefficient <> aPoly.asList( )

Copyright © 2006 The McGraw-Hill Companies, Inc. def __str__(self): """return string representation""" r = "" p = len(coefficient) + 1 while p > 0: p = p - 1 if coefficient[p] == 0: continue if p < len(coefficient): r = r + "+" r = r + str(coefficient[p]) if p == 0: continue r = r + "x" if p <= 1: continue