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Types in Scripting Languages

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.

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Types in Scripting Languages

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  1. Types in Scripting Languages CS 351 – Programming Paradigms

  2. 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”

  3. Data Types in Python • Python uses the reference model for its types. • Some built-in types in Python include: Type Kind Syntax Example str String ‘hello‘ list Sequence [4.0, 'string', True] tuple Sequence (4.0, 'string', True) set Set set([4.0, 'string', True]) dict Mapping {'key1': 1.0, 'key2': False} int Integer 42 float Number 3.1415927

  4. 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.

  5. 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]

  6. 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?

  7. 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 = 12345 def printsomething(self): return “hello world” • We can create objects simply: x = myclass() print x.printsomething()

  8. 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?

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

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