(P1/2) COMP 1126 - Functions and Scope

callable

any object that can be invoked using parentheses to perform a task

State how callables improve abstraction

They allow tasks to be initiated without focusing on their execution logic

invocation

the act of executing a callable

Explain passing

Passing is when specific date is placed within the parentheses, fitting the constraints of placeholder values known as parameters. Passing values into the parentheses creates arguments which act as their respective placeholder values in the function. Each parameter/argument is separated by a comma

delimiter

character used to separate pieces of data

function

callable objects whose sole purpose is to execute a isolated routine

isolated routine

sequenced instructions that have been packaged into a single unit

user-defined functions

those encapsulating a block of code created by a programmer

built-in functions

predefined functions created by a developer of the programming language which require no setup on behalf of the user

State the reasons why user-defined functions are beneficial (5)

They simplify tasks — breaking down components of complex tasks

Abstract operations — due to their nature as callable objects

Reusable — each time they are invoked, the same routine is called

Shareable — They can be recreated in other scripts

Increases readability — Indicating which components of a script are to be executed alongside each other

State the rules for creating user-defined functions in Python

Names cannot be keyword or contain spaces

The first character must be a letter in the English alphabet or an underscore

Following characters must be a letter in the English alphabet, an underscore or a numerical digit (0-9)

recursion

method of problem-solving in which a function calls itself to solve a smaller piece of a larger problem

State and describe the three main components of recursion

Base case — the stopping condition that ends the recursion and prevents the function from calling itself infinitely

Recursive case — the part where the function breaks the problem down into a smaller version of itself and calls the function again

Call stack - -the memory area where the computer tracks active function calls using a LIFO structure

State and describe the two main types of recursion

Head — the function makes its recursive call first. The calculations or operations for the current frame are put on hold until the recursive call returns

Tail — the recursive call is the absolute final action. No calculations are performed after the call returns

scope

the region within a program in which an object is accessible

State and describe the four types of scope

Local — objects which are defined within a function and are only accessible when that function runs.

Enclosed — objects which are in the outer function of an inner function and are also accessible within the latter

Global — objects defined at the top-level of the script which are accessible anywhere

Built-in — Objects which are pre-defined in Python and are accessible universally

State how the different scopes play a part in enhancing abstraction in Python

Local and enhanced — Aid encapsulation as it allows temporary variables to exist and be unmodifiable outside of the execution of their respective function, secluding them from the program as a whole

Global — Aid abstraction as it reduces the amount of parameters a function has to accept in the cases where the same value is used across multiple functions

Built-in — Being universally accessible inherently aids abstraction as built-in function perform predefined tasks and the alternative of defining their instructions would introduce complexities to the program

Describe lexical scoping

It refers to the accessibility of a variable in respect to its location in the code at runtime. Python uses the LEGB for variable lookup where it checks each scope one-by-one from local to enclosed to global to built-in, stopping once it finds a match