Chapter 6

Question 1

Functions as abstraction mechanisms

Answer 1

-Abstraction- hides detail, allowing person to view many things as one thing
-Example of everyday tasks: doing my laundry

Question 2

Functions eliminate__

Answer 2

redundancy

Question 3

Functions hide__

Answer 3

complexity
- a function call expresses the idea of a process to the programmer w/o forcing him/her to wade through the complex code that realizes that idea

Question 4

Functions Support ___ with Systematic Variations

Answer 4

• General Method: a method that solves a class of problems, not just one individual problem
• problem instances: individual problems that make up a class of problems
• Algorithms should be general enough to provide a solution to many problem instances
• A function should provide a general method with systematic variations

Question 5

Functions support the ___

Answer 5

• Division of labor
• Each function should perform a single coherent task
• Example: Computing a summation
• Each of the tasks required by a system can be assigned to a function
• Including the tasks of managing or coordinating the use of other functions

Question 6

Top-down design

Answer 6

• Starts with a global view of the entire problem and breaks the
  problem into smaller, more manageable subproblems (problem decomposition)
• As each subproblem is isolated, its solution is assigned to a function
• As functions are developed to solve subproblems, solution to overall problem is gradually filled out (stepwise refinement)

Question 7

Structure chart

Answer 7

• a diagram that shows the relationship among a program’s
  functions and the passage of data between them
• Each box in the structure is labeled with a function name
  *The main function at the top is where the design begins
  *Lines connecting the boxes are labeled with data type names
  *Arrows indicate the flow of data between them

Question 8

recursive design

Answer 8

the process of decomposing a problem into subproblems of exactly the same form that can be solved by the same algorithm

Question 9

recursive function

Answer 9

a function that calls itself
-To prevent function from repeating itself indefinitely, it must contain at least one selection statement

Question 10

base case

Answer 10

the condition in a recursive algorithm that is tested to halt the recursive process

Question 11

selection statement

Answer 11

examines base case to determine whether to stop or to continue with another recursive step.

Question 12

recursive definition

Answer 12

-a set of statements in which at least one statement is defined in terms of itself.
-consists of equations that state what a value is for one or more
base cases and one or more recursive cases

Question 13

infinite recursion

Answer 13

-in a running program, the state that occurs when a recursive method cannot reach a stopping state
-arises when programmer fails to specify base case or to
reduce size of problem in a way that terminates the recursive process

Question 14

PVM reserves an area of memory for the ____

Answer 14

call stack

Question 15

For each call of a function, the PVM must allocate on the call stack a _____

Answer 15

stack frame

Question 16

A stack frame contains____

Answer 16

• Values of the arguments
• Return address for the particular function call
• Space for the function call’s return value

Question 17

When a call returns, ________ is used to locate the next instruction, and stack frame is deallocated

Answer 17

return address

Question 18

T or F: Amount of memory needed for a loop grows with the size of the problem’s data set

Answer 18

F: Amount of memory needed for a loop does not grow with the size of the problem’s data set

Question 19

namespace

Answer 19

the set of all of a program’s variables and their values
- can be controlled with good design principles

Question 20

____ and _____ receive their values as soon as they are introduced

Answer 20

• Module variables
• temporary variables

Question 21

____ behave like a variable and are introduced in a function or method header

Answer 21

• Parameters
• Do not receive a value until the function is called

Question 22

method names

Answer 22

a method reference always uses an object followed by a dot and the method name
ie:
sentence.split()

Question 23

scope

Answer 23

the area of a program text in which the value of a variable is visible

Question 24

Scope of temp variables

Answer 24

• Area of code in the body of the function just below where each variable is introduced
• restricted to the body of the functions in which they are introduced and invisible elsewhere in a module

Question 25

Scope of parameter

Answer 25

• the entire body of the function
• invisible outside function definition

Question 26

Scope of module variables

Answer 26

• includes entire module below point where they are introduced
• also includes the nested bodies of other function def that occur earlier
• A function can reference a module variable, but can’t under normal circumstances assign a new value to it

Question 27

What happens when a Python function assigns a new value to a module variable?

Answer 27

• When such an attempt is made, the PVM creates a new, temporary variable of the same name within the function
• variable does not change, still remains the value it was assigned outside of function

Question 28

Variable’s lifetime

Answer 28

Period of time when variable has memory storage
associated with it
- When a variable comes into existence, storage is allocated for it; when it goes out of existence, storage is reclaimed by the PVM

Question 29

T or F: Module variables come into existence when introduced and generally exist for lifetime of program that introduces or imports them

Answer 29

True

Question 30

__ and __ come into existence when bound to values
during call, but go out of existence when call terminates

Answer 30

Parameters and temporary variables

Question 31

A functions arguments

Answer 31

• provide the function’s caller with the means of transmitting
  information to the function

Question 32

optional arguments

Answer 32

• can specify optional args with default values in any function definition
• syntax:
  def <function>(<required>,
  <key‐1> = <val−1>, ... <key−n> = <val−n>)</required></function>
• Following the required args are one or more default or keyword args
• When function is called with these args, default values are overridden by caller’s values

Question 33

Default args can be supplied in 2 ways which are?

Answer 33

1. By position
2. By keyword

Question 34

higher‐order function

Answer 34

• expects a function and a set of data values as arguments and/or returns functions as values
• Argument function is applied to each data value and a set of results or a single data value is returned
• separates task of transforming each data value from logic of accumulating the results

Question 35

T/F: Functions can be assigned to variables, passed as arguments, returned as the values of other functions, and stored in data structures

Answer 35

True

Question 36

T/F: Passing a function as an argument is different from passing any other datum

Answer 36

False: Passing a function as an argument is no different from passing any other datum

Question 37

Mapping

Answer 37

• applies a function to each value in a sequence and returns a new sequence of the results

Question 38

Filtering

Answer 38

a function called a predicate is applied to each value in a list
- If predicate returns True, value is added to a new list; otherwise, value is dropped from consideration

Question 39

reducing

Answer 39

we take a list of values and repeatedly apply a function to accumulate a single data value

Question 40

Lambda

Answer 40

• an anonymous function
• When the lambda is applied to its arguments, its expression is evaluated and its value is returned
• syntax of lambda is very tight and restrictive:
  lambda <argname−1, …, argname−n>: <expression></expression>
• All of the code must appear on one line and it cannot
  include a selection statement, because selection statements are not expressions

Question 41

jump table

Answer 41

is a dictionary of functions keyed by command names