Python Midterm Prep Multiple Choice (copy)

Two types of files

Two types of files

Text file (contains data that's been encoded as text)

Two ways to access data stored in file

Sequential access (file read sequentially from beginning to end, can't skip ahead)
Direct access (can jump directly to any piece of data in the file)

open function

used to open a file; creates a file object and associates it with a file on the disk

file_object = open(filename, mode)

Mode

string specifying how the file will be opened (r=reading, w=writing, a=appending)

Method

a function that belongs to an object

ex. file_variable.write(string)

close using the .close() method

read method

file object method that reads entire file contents into memory

readline method

file object method that reads a line from the file

read position

marks the location of the next item to be read from a file

when open file with 'w' mode, if the file already exists

it is overwritten

dictionary

object that stores a collection of data (each element consists of a key and a value)

-key must be an immutable object

-dictionaries are mutable

general format for retrieving value from dictionary

dictionary[key]

dictionaries are mutable, to add a new key-value pair:

dictionary[key] = value

len function

used to obtain number of elements in a dictionary

to create an empty dictionary

{}

or built-in function dict ()

items method

returns all the dictionaries keys and associated values

clear method

deletes all the elements in a dictionary, leaving it empty

get method

gets a value associated with a specified key from the dictionary

keys method

returns all the dictionaries keys as a sequence

pop method

returns value associated with specified key and removes that key-value pair from the dictionary

values method

returns all the dictionaries values as a sequence

popitem method

returns a randomly selected key=value pair and removes that key-value pair from the dictionary

Key

always on the left side (always a text/in quotes)

value

always on right (can be any Python object)

list needs ______ value, dictionary needs _____ value

index , key

KeyError

didn't find a match for your key/doesn't exist in dictionary

Will a key repeat in a dictionary?

No, keys are unique "updates the value"

Procedural Programming

writing programs made of functions that perform specific tasks

Object-oriented programming

focused on creating objects

Object

entity that contains data and procedures

Objects have methods and attributes

procedures are methods, data is attributes

Data hiding

objects data attributes are hidden from code outside the object (access restricted to the object's method)

Object reusability

the same object can be used in different programs

an instance

something that belongs to a class/an object created from a class

Class

code that specifies the data attributes and methods of a particular type of object

Class definition

set of statements that define a class's methods and data attribute

"self" parameter

required in every method in the class-references specific object that the method is working on (always first parameter that we need)

objects state

the values of the object's attribute at a given moment

Mutator method

(set method) allows you to change the value of an attribute

Accessor method

(get method) returns value of an attribute

Instance attribute

belongs to a specific instance of a class (if many instances of a class are created, each would have its own set of attributes)

passing objects as arguments

when you pass an object as an argument, you are actually passing a reference to the object

UML diagram

standard diagrams for graphically depicting object-oriented systems

Inheritance

used to create an "is a" relationship between classes, exists when one object is a specialized version of another object

Superclass

base class/general class

Subclass

derived/specialized class (extended version of superclass)

(superclass name is placed in parentheses after subclass name)

polymorphism

an objects ability to take different forms

Initializer method

calls initializer method of superclass and then initializes unique data attributes (superclass cannot access methods in subclass, BUT subclass can access any methods in superclass) (cannot create a subclass without first creating the superclass)

Hidden attributes

are not passed on in inheritance (if you hide it in the parent it won't be passed)

User Interface

the part of the computer with which the user interacts

Command line interface

displays a prompt and the user types a command that is then executed

Graphical User Interface (GUI)

allows users to interact with a program through graphical elements on the screen; event-driven (the user determines the order in which things happen)

tkinter module

allows you to create simple GUI programs

Widget

graphical element that the user can interact with or view

__init__method

builds the GUI

Label widget

displays a single line of text in a window

pack method

determines where a widget should be positioned and makes it visible when the main window is displayed

Frame widget

container that holds other widgets

Button widget

widget that the user can click to cause an action to take place

Info dialog box

a dialog box that shows information to the user

Quit button

create a Button, set the root widgets destroy method as callback function

Entry widget

rectangular area that the user can type text into

IntVar class can be used along with

Radiobutton widgets

The readline method

uses a sentinel when the end of a file is reached

encapsulation

a self contained unit combining data and code into single objects