FUNCTIONS.pptx

Introduction
 Large programs are often difficult to manage, thus large programs are
divided into smaller unitsknownas functions.
 It issimply a group of statements under any namei.e. function nameand canbe
invoked(call) from other part of program.
 T
ake an example of School Management Software, now this software will
contain various tasks like Registering student, Fee collection, Library book issue,
TC generation, Result Declaration etc. In this case we have to create different
functionsfor eachtask to manage the software development.

Introduction
 Set of functions is stored in a file called MODULE. And this approach is
knownasMODULARIZATION, makesprogram easier to understand,test
and maintain.
 Commonly used modules that contain source code for generic need are
called LIBRARIES.
 Modulescontains setof functions.Functionsisof mainly two types:
Built-in Functions

Advantages of Function
 PROGRAM HANDLING EASIER: only small part of the program is dealt with
at a time.
 REDUCEDLoC:aswith functionthe commonsetof code iswritten only onceand
canbe called from any part of program, soit reducesLineof Code
 EASY UPDATING : if function is not used then set of code is to be repeated
everywhere it is required. Hence if we want to change in any
formula/expression then we have to make changes to every place, if
forgotten then output will be not the desired output. With function we have to

UserDefinedFunctions
 A function is a set of statements that performs a specific task; a common
structuring elements that allows you to use a piece of code repeatedly in
different part of program. Functions are also known as sub-routine, methods,
procedure or subprogram.
 Syntax to create USERDEFINEDFUNCTION
def function_name([commaseparated list of parameters]):
statements…. statements….
KEYWORD FUNCTIONDEFINITION

Pointstoremember…
 Keyword def marksthe start of function header
 Functionnamemustbe uniqueand follows namingrules sameasfor
identifiers
 Functioncantake arguments.It isoptional
 A colon(:) to mark the end of function header
 Functioncancontainsoneor morestatementto perform specific task
 Anoptional returnstatementto return a value from the function.
 Functionmustbe called/invoked to execute its code

UserDefined function can be….
1. Functionwith noargumentsand noreturn
2. Function with argumentsbut no returnvalue
3. Function with argumentsand return value
4. Function with no argument but return value

Function with no argument and no return
 Thistype of function isalso knownasvoid function
FUNCTIONNAME NO P
ARAMETER,HENCEVOID
Returnkeyword notused
FUNCTIONCALLING,ITWILLINVOKEwelcome()TO PERFORMITSACTION

Functionwithparametersbutno return value
 Parametersare given in the parenthesisseparated by comma.
 Valuesare passedfor the parameter at the time of function
calling.

Functionwithparametersbutno return value

Functionwith parameter and return
 We canreturn values from function usingreturn
keyword.
 Thereturn value mustbe usedat the calling place by
–
 Eitherstore it any variable
 Usewith print()
 Usein any expression

Functionwithreturn
NOTE:the return statement ends a
functionexecutionevenif it is inthe
middleof function. Anythingwritten
below return statement will
become unreachable code.
def max(x,y):
if x>y:
returnx
else:
returny
print(“Iam not reachable”)

ParametersandArgumentsin Function
 Parameters are the value(s) provided in the parenthesis when we write
function header. Theseare the values required by function to work
 If there are morethan oneparameter, it mustbe separated by comma(,)
 An Argument is a value that is passed to the function when it is called. In
other words arguments are the value(s) provided in function call/invoke
statement
 Parameter isalso knownasFORMAL ARGUMENTS/PARAMETERS
 Arguments is also known as ACTUAL ARGUMENTS/PARAMETER
 Note: Functioncanalter only MUTABLETYPEvalues.

Exampleof Formal/Actual Arguments
ACTUALARGUMENT
FORMALARGUMENT

TypesofArguments
 Thereare 4 types of ActualArguments allowed in
Python:
1. Positional arguments
2. Default arguments
3. Keyword arguments
4. Variable length arguments

Positional arguments
 Are argumentspassedto a function in correct positional
order
 Here x ispassedto a and y ispassedto b i.e. in the order of their position

IfthenumberofformalargumentandactualdiffersthenPythonwillraiseanerror

Default arguments
 Sometimes we can provide default values for our positional
arguments. In this case if we are not passing any value then default
valueswill be considered.
 Default argumentmustnotfollowed by non-default arguments.
def interest(principal,rate,time=15):
def interest(principal,rate=8.5,time=15):
def interest(principal,rate=8.5,time):
VALID
INVALID

Keyword(Named)Arguments
 The default keyword gives flexibility to specify default value for a
parameter so that it can be skipped in the function call, if needed.
However, still we cannot change the order of arguments in function
call i.e. you have to remember the order of the arguments and pass
the value accordingly.
 T
oget control and flexibility over the values sent as arguments, python
offers KEYWORDARGUMENTS.
 This allows to call function with arguments in any order using name of

Rules forcombining all threetypeof
arguments
 Anargumentlist mustfirst contain positional arguments
followed by keyword arguments
 Keyword argumentsshouldbe taken from the required
arguments
 Y
oucannotspecify a value for an argumentmore than once

Exampleof legal/illegal function call
FUNCTION CALL LEGAL/
ILLEGAL
REASON
Average(n2=20, n1=40,n3=80) LEGAL Nondefault values provided as
named arguments
Average(100,200,n1=300) LEGAL Keyword argument canbe in any
order
Average(100,n2=10,n3=15) LEGAL Positional argument before the
keyword arguments
Average(n3=70,n1=90,100) ILLEGAL Keyword argument before the
positional arguments
Average(100,n1=23,n2=1) ILLEGAL Multiple values provided for n1
def Average(n3,n2,n1=200):
return(n1+n2+n3)/3

ReturningMultiple values
 Unlikeother programming languages,python lets youreturn
morethanonevalue from function.
 Themultiple return value mustbe either stored in TUPLEor wecan
UNP
ACKthe received value by specifying the samenumberof
variables onthe left of assignmentof function call.

Multiple return value stored in TUPLE

Multiple return value stored by
unpacking in multiple variables

Scopeof
Variables
 SCOPE means in which part(s) of the program, a
particular piece of code or data isaccessible or known.
 InPython there are broadly 2 kinds of Scopes:
Global Scope
Local Scope

Global Scope
 A name declared in top level segment( main ) of a program is
said to haveglobal scopeand canbe usedin entire program.
 Variable defined outsideall functionsare global variables.
 Aname declare in a function body is said to have local scope i.e. it can be
usedonly within this function and the other block inside the function.
 Theformal parameters are also having local scope.
Local Scope

Example– Localand Global Scope

“a‟isnot accessible
here becauseit is
declared infunction
area(), soscopeis
local to area()

Variable "ar‟ is accessible in
function showarea() because
it ishaving Global Scope

Thisdeclaration “global count” is
necessaryfor usingglobal
variables in function, other wise an
error “local variable 'count'
referenced before assignment”
will appear becauselocal scope
will create variable “count” and it
will be found unassigned

Lifetime of Variable
 Isthe time for whicha variable livesinmemory.
 For Global variables the lifetime isentire program run
i.e. aslong asprogram isexecuting.
• For Local variables lifetime is their function‟s run i.e. as long as
function isexecuting.

NameResolution(ScopeResolution)
 Forevery nameusedwithin program python follows nameresolutionrules knownasLEGB rule.
 (i) LOCAL : first check whether name is in local environment, if yes Python uses its value
otherwise moves to (ii)
 (ii) ENCLOSING ENVIRONMENT: if not in local, Python checks whether name is in Enclosing
Environment,if yes Python uses its value otherwise moves to (iii)
 GLOBAL ENVIRONMENT: if not in above scope Python checks it in Global environment, if yes
Python uses itotherwise moves to (iv)
 BUILT-IN ENVIRONMENT: if not in above scope, Python checks it in built-in environment, if
yes, Python uses its value otherwise Python would reportthe error:
 name<variable> notdefined

Predict the output
Programwith
variable “value” in
both LOCALand
GLOBALSCOPE

Predict the output
UsingGLOBAL
variable “value” in
local scope

Predict the output
Variable “value”
neither in local nor
global scope

Predict the output
Variable in Global
notin Local
(input in variable at
global scope)

Mutability/Immutability of
Arguments/Parameters and function call

 Fromthe previous example we can recall the concept learned in classXI
that Python variables are not storage containers, rather Python
variables are like memory references, they refer to memory address
where the value is stored, thus any change in immutable type data
will also change the memory address. So any change to formal
argument will not reflect back to its corresponding actual argument
and in case of mutable type, any change in mutable type will not
change thememory address of variable.

Because List if Mutable type, hence any change in formal
argument myList will not change the memory address, So
changes done tomyListwill be reflectedback to List1.
Howeverif weformalargumentisassignedtosomeothervariableordatatype then
linkwillbreakandchangeswillnotreflectbacktoactualargument
Forexample (if inside function updateData() we assign myList as:
myList = 20 OR myList = temp

PassingString to function
 Functioncanaccept string asa parameter
 As per Python, string is immutable type, so function can access the
value of string but cannotalter the string
 T
o modify string, the trick is to take another string and concatenate
the modified value of parameter string in the newly created string.

Passing string tofunction and counthow
many vowels in it

Program to counthowmanytimesany
character ispresent in string

Program toJumblethegiven string by passing itto
functionusing temporary string

PassingListto function
 We canalso passListto any function asparameter
 Dueto the mutable nature of List,function canalter the list of
valuesin place.
 It ismostlyusedin data structurelike sorting, stack, queue etc.

Passing list tofunction,and just
double each value

Passinglist to functionto double the odd
valuesand half the even values

Passingnested list to function and print all thosevalues
whichare at diagonal position in the form of matrix

Passinglist to functionto calculate sumand average of
all numbersand return it in the form of tuple

Passingtuples to function
 We can also passtuples to function as parameter
 Dueto its immutability nature, function can only access
the values of tuples but cannot modify it.

Creating a login program with the
help of passing tuple to
function

Creating a login program with the
help of passing tuple to
function
OUTPUTOFPREVIOUSPROGRAM

Input n numbers in tuple and pass it function to
count howmanyevenand odd numbersare
entered.

PassingDictionary to function
 Pythonalso allows usto passdictionaries to function
 Dueto its mutability nature,function canalter the keysor values
of dictionary in place
 Letusseefew examples of howto passdictionary to functions.

P
assing dictionary to function with list and stores the
value of list as key and its frequency or no. of
occurrenceasvalue

Passingdictionary to function with keyand value,
and update value at that key in dictionary

FUNCTIONS.pptx

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FUNCTIONS.pptx