A crash course in Python - Lesson 6: Object-oriented programming

Python allows the programmer to define classes that encapsulate:

• attributes (i.e., data that describe the status of the instantiated object)
• methods (i.e., functions that describe the behavior of the instantiated object)

Suppose we want to create a class that describes a set of elements (although, as we saw in a previous lesson, Set is already a built-in Python data structure.

The behavior that we may apply on such class is as follows:

• adding items
• removing items from it
• check whether it contains a certain value

Here is a possible implementation of such class:

class Set:
    def __init__(self, values=None):  # constructor
        self.dict = {}
        if values is not None:
            for value in values:
                self.add(value)

    def __repr__(self):  # toString() method
        return "Set: " + str(self.dict.keys())

    def add(self, value):
        self.dict[value] = True

    def contains(self, value):
        return value in self.dict

    def remove(self, value):
        del self.dict[value]

Then we can use such class as follows:

s = Set([1,2,3])

s.add(4)
print s.contains(4)  # True

s.remove(3)
print s..contains(3)  # False