Types in Scripting Languages CS 351 – Programming Paradigms

Data Types in Python Scripting languages don’t generally require or allow the declaration of types ofr variables. Most perform a series of run-time checks to make sure that values are used in an appropriate way. Python is strongly typed with operations enforced at run-time. The type system is Python is known as ``duck typing’’. This informally allows the type of a value to be determined via the following rule: “If looks like a duck and quacks like a duck, it is a duck”

Data Types in Python Python uses the reference model for its types. Some built-in types in Python include: TypeKindSyntax Example strString‘hello‘ listSequence[4.0, 'string', True] tupleSequence(4.0, 'string', True) setSetset([4.0, 'string', True]) dictMapping{'key1': 1.0, 'key2': False} intInteger42 floatNumber

Examples s = “hello” r = 56 l = [1,2,3] t = (56,78,54) dict = { ‘one’ : 1, ‘two’:2 } We can just initialise the types and the interpreter takes care of the rest.

Lists in Python Lists can form the basic blocks of most complex data structures in Python. l = [1,2,3,4] l.append(5) print l # prints [1,2,3,4,5] l.pop print l # prints [1,2,3,4] l.pop(0) print l # prints [2,3,4]

Lists and the filter and map functions We can define an arbitrary function def f(x): return x%2==0 filter ( f, range ( 2, 100 ) ) Defining another function: def g(x): return x+4 map ( g, range (4, 16) ) What are doing here? What paradigm is this?

Object Orientation Python is explicitly object-oriented. To define a class in Python we use the following syntax: class myclass: “This class shows Python Syntax” intval = def printsomething(self): return “hello world” We can create objects simply: x = myclass() print x.printsomething()

Object Orientation The constructor for a Python class has special syntax. class myclass: def __init__ (self, list ) : self.data = list# assign list to data x = myclass ( [1,2,3,4,5] ) print x.data# what is printed?

Object Orientation class Shape: def __init__ (self) : self.name = “Shape” def printName (self) : return self.name def getArea (self ) : return 0