Cs 1110 Prelim 2 Terminology

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Accumulator

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A variable in a for-loop that stores information computedin the for-loop, which will be still available when the for-loop is complete

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Attribute

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A variable stored inside an object

Note: It is impossible to enforce invariants on attributes as any value can be stored in an attribute at any time

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Bottom-Up Rule

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When trying to access a attribute stored inside of an object or use a method stored in a class, it first looks in the object folder, then the object class, then the parent class and so on

Note: If python does not find the attribute or method then it results in an error

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Class

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A class is a type not built into python, and a value of said type is an object

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What goes in the class definition?

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class classname(superclass):

Specification

Getters and Setters

Initializer

Methods

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Constructor

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A function that creates an object for a class

Note: A constructor has the same name as the type of object being created

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What happens when a constructor is called?

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The constructor:

creates an empty folder,

puts it in heap space,

calls the initializer method,

and returns the object name as the value of the final expression

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Default Argument

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A value that is given to a parameter if the user does not provide that parameter

Example: foo(x,y=2,z=3)

foo(1,z=4) and foo(1,5) are valid function calls

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Dispatch on Type

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A function that can take multiple types of input, and its behavior depends on the type of input

Note: Also used in try-excepts to determine whether to recover from an error

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Duck Typing

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This is a less effective way of determining if an object is a certain type by checking to see if it has attributes and methods of the right names

Note: If it looks like a duck and if it quacks like a duck, then it is a duck

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Encapsulation

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Hiding data or implementation to prevent them from being accessed by users who do not need them

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Getter

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This is a method that is used to access a hidden attribute, ensuring that it does not get changed

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Global Space

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The area of memory that stores any variable not defined in the body of a function

Note: These variables exist until you either erase them manually or quit python

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Heap Space

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The area of memory that stores mutable objects

Note: The objects can only be accessed directly, via a variable in global space or a call frame with the value of the object name

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Immutable Attribute

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A hidden attribute that has a getter, but no setter, making it so the user cannot change the attribute

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Implementation

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The details of a collection of python code that are unimportant to other users of this module or class

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What does the implementation include?

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The bodies of all functions or methods, hidden functions and hidden methods, and hidden attributes

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Inheritence

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The process by which a class inherits the attributes and methods of its parent class if the attribute and/or method was not mentioned in the class definition

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Interface

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The collection of python code that the user sees when they type help(module or class name)

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What does the interface include?

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A list of the class names, all of the unhidden attributes, and all of the unhidden function or method names with their specifications

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Invariant

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A statement about an attribute that must always be true

Note: similar to a precondition, the invariant can ensure that certain types of values are not assigned to the attribute

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The operator "is"

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This is like the operator == except that it compares class names rather than contents

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Method

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A function stored inside a class folder

Note: A method is called by typing the object name followed by a dot before the function name

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Mutable Attribute

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A hidden attribute that has both a getter and a setter

Note: the attribute can be changed by the user as long as the invariant is not violated

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Object

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A value whose type is a class, typically containing attributes and methods

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Operator Overloading

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The means by which python evaluates the various operator symbols, such as +, *, and /

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Overriding a Method

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The act of redefining a method previously defined in a parent class

Note: an overridden method is called by typing the name of the super class followed by a dot then the method name

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Property

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A special way of creating getters and setters, with its value stored in an associated attribute

Note: I don't think we need to know this

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Setter

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A special method that can change the value of an instance attribute of the same name

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Subclass

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A class that extends another class

Note: If D is a subclass of C, then D inherits all the attributes and methods from C as well as its own attributes and methods declared in D

Note: Every user defined class must extend another class

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Limited Try-Except Statement

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A Try-Except statement that only recovers from certain types of errors

Note: It takes the form:

Try:

statements

Except error-class:

statements