Chapter 6 Flashcards
Functions as abstraction mechanisms
-Abstraction- hides detail, allowing person to view many things as one thing
-Example of everyday tasks: doing my laundry
Functions eliminate__
redundancy
Functions hide__
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
Functions Support ___ with Systematic Variations
- 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
Functions support the ___
- 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
Top-down design
- 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)
Structure chart
- 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
recursive design
the process of decomposing a problem into subproblems of exactly the same form that can be solved by the same algorithm
recursive function
a function that calls itself
-To prevent function from repeating itself indefinitely, it must contain at least one selection statement
base case
the condition in a recursive algorithm that is tested to halt the recursive process
selection statement
examines base case to determine whether to stop or to continue with another recursive step.
recursive definition
-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
infinite recursion
-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
PVM reserves an area of memory for the ____
call stack
For each call of a function, the PVM must allocate on the call stack a _____
stack frame
A stack frame contains____
- Values of the arguments
- Return address for the particular function call
- Space for the function call’s return value
When a call returns, ________ is used to locate the next instruction, and stack frame is deallocated
return address
T or F: Amount of memory needed for a loop grows with the size of the problem’s data set
F: Amount of memory needed for a loop does not grow with the size of the problem’s data set
namespace
the set of all of a program’s variables and their values
- can be controlled with good design principles
____ and _____ receive their values as soon as they are introduced
- Module variables
- temporary variables
____ behave like a variable and are introduced in a function or method header
- Parameters
- Do not receive a value until the function is called
method names
a method reference always uses an object followed by a dot and the method name
ie:
sentence.split()
scope
the area of a program text in which the value of a variable is visible
Scope of temp variables
- 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
Scope of parameter
- the entire body of the function
- invisible outside function definition
Scope of module variables
- 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
What happens when a Python function assigns a new value to a module variable?
- 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
Variable’s lifetime
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
T or F: Module variables come into existence when introduced and generally exist for lifetime of program that introduces or imports them
True
__ and __ come into existence when bound to values
during call, but go out of existence when call terminates
Parameters and temporary variables
A functions arguments
- provide the function’s caller with the means of transmitting
information to the function
optional arguments
- 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
Default args can be supplied in 2 ways which are?
- By position
- By keyword
higher‐order function
- 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
T/F: Functions can be assigned to variables, passed as arguments, returned as the values of other functions, and stored in data structures
True
T/F: Passing a function as an argument is different from passing any other datum
False: Passing a function as an argument is no different from passing any other datum
Mapping
- applies a function to each value in a sequence and returns a new sequence of the results
Filtering
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
reducing
we take a list of values and repeatedly apply a function to accumulate a single data value
Lambda
- 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
jump table
is a dictionary of functions keyed by command names
