3 cs xii_python_functions _ parameter passing

.
Class-XII Computer Science (083)
All the contents used as part of the slides are either self created or from the public domain or textbooks for Class XII.
This presentation is only used for leaning purpose only. Programs used in this presentation are based on Python 3.8.0.
Computational Thinking and Programming - 2
Working with Functions
Parameter Passing
S K Mahto, PGT (Computer Science)
J.N.V East Medinipur WB

Parameter Passing
● We can pass values to functions, for this we need to define variables to receive
values in function definition and we can send value via a function call statement.
● For example
Presented by : S K Mahto, PGT Computer Science

Parameter Passing
● Pass by reference vs. value
● All parameters (arguments) in the Python language are passed by reference.
● It means if we change what a parameter refers to within a function, the change
also reflects back in the calling function.
● For example −

Parameter Passing
● Pass by reference vs. value

Parameter Passing
● Pass by reference vs. value --- continue
There is one more example
where argument is being
passed by reference and the
reference is being overwritten
inside the called function.

Parameter Passing
def fact(num):
f=1
for i in range(num,0,-1):
f=f*i
return(f)
print(fact(5))
Body of the
function
Name of
the
function
Argument of the function
Function call
OR
Calling function
Actual Parameter
Vs.
Formal Parameter
Here num is formal parameter/ argument
(parameter used in function
definition is called formal parameter)
Here 5 is actual parameter/ argument
(parameter used in calling function
is called actual parameter)

Parameter Passing
● Python supports three types of formal arguments/ parameters :
1. Positional (required) arguments
2. Default arguments
3. Keyword (or named) arguments
4. Variable length arguments

Parameter Passing
Positional (required) arguments
Positional (Required) arguments are the arguments passed to a function in correct positional order. Here, the
number of arguments in the function call should match exactly with the function definition.
To call the function printme(),
we definitely need to pass one
argument otherwise it gives a
syntax error as follows -

Parameter Passing
Default arguments
● A default argument is an argument that assumes a default value if a
value is not provided in the function call for that argument. The
following example gives an idea on default arguments, it prints
default age if it is not passed −

Parameter Passing
Default arguments

Parameter Passing
Keyword arguments
● Keyword arguments are related to the function calls. When we use keyword
arguments in a function call, the caller identifies the arguments by the parameter
name.
● This allows us to skip arguments or place them out of order because the Python
interpreter is able to use the keywords provided to match the values with
parameters.
● We can also make keyword calls to the printme() function in the following ways −

Parameter Passing
Keyword arguments
Output

Parameter Passing
Keyword arguments -- continue…..
● The following example gives more clear picture.
● Note that the order of parameters does not matter.

Parameter Passing
Rules for combining all three types of arguments-
Python states that in a function call statement :
● An argument list must first contain positional (required ) arguments followed by
any keyword argument.
● Keyword arguments should be taken from the required arguments preferably.
● We can not specify a value for an argument more than once.
Example….

Parameter Passing
Rules for combining all three types of arguments-
Output

Parameter Passing
Variable length arguments
● You may need to process a function for more arguments than you specified while
defining the function. These arguments are called variable-length arguments and
are not named in the function definition, unlike required and default arguments.
● Syntax for a function with non-keyword variable arguments is this −
An asterisk (*) is placed before the variable name that holds the values of all nonkeyword
variable arguments. This tuple remains empty if no additional arguments are specified during
the function call. Example…..

Parameter Passing
Variable length arguments

Parameter Passing
RETURNING VALUES FROM FUNCTIONS
Functions may or may not return a value.
1. Functions returning some value (Non-void functions)
return(value) OR return value
value may be - literal / variable / expression
2. Functions not returning any value (Void functions)
return
Function styles –
1. No argument, No return value
2. No argument with return value
3. Argument , Without return value
4. Argument with return value

Parameter Passing
RETURNING MULTIPLE VALUES
To return multiple values from function we have to ensure the following things –
1. The return statement inside a function body in the form of -
return value1, value2,…
2. The function call statement should receive or use the returned values in one of
the following ways –
- in the form of tuple variable
def squared(2,3,4):
return x*x,y*y,z*z
t=squared(2,3,4)
print(t)

Parameter Passing
RETURNING MULTIPLE VALUES
- by specifying the same number of variable on left hand side of the
assignment in function call.
def squared(2,3,4):
return x*x,y*y,z*z
v1,v2,v3=squared(2,3,4)
print(v1,v2,v3)

3 cs xii_python_functions _ parameter passing

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