[Susan Thomson]

13/06/2018 at 9:20 am

I am looking for some advice with parameter passing in Python. In the following example, exactly which parameters are the formal parameters and which are the actual parameters?

Do I include the OUT parameters? or is it only applied to the parameters in brackets?

# area of rectangle in modules

def get_inputs():
length = int(input(“Enter the length : “))
breadth = int(input(“Enter the breadth : “))
return length, breadth

def calculate_area(length, breadth):
area = length * breadth
return area

def display_area(area):
print(“Area :”,area)

# main program
length, breadth = get_inputs()
area = calculate_area(length, breadth)
display_area(area)

[Alan]

13/06/2018 at 9:36 am

Hi Susan

I would say that in your example you have all actual parameters, as the same variable names are used throughout.

If you change the ‘calculate_area’ procedure to something like…

def calculate_area(L, B):
result = L * B
return result

And leave the rest the same then you will have some more obvious formal parameters e.g. ‘L’, ‘B’ and ‘result’.

[Mr Stagg]

13/06/2018 at 9:40 am

Actual – the parameters being passed
Formal – the ones in the brackets in the function – being formally defined in the function

thats how i teach it anyhow – its in the formality of the theory where python falls down – vb easy as byref and data types defined in the function line.

Harry

[Susan Thomson]

13/06/2018 at 9:40 am

Many thanks for the reply Alan.

I am just getting used to Python. Does this also mean that in the calling statements, the length, breadth and area (used in the assignments) are also actual parameters?

I used Visual Basic before and the actual parameters were more obvious.

Many thanks in advance

[Peter Thoresen]

13/06/2018 at 9:58 am

Algorithms will use in/out/in-out to show the flow of data – but this is for design only.

Formal and Actual parameters only apply in the implementation.

Your “getinput” function does have data coming out, but it has NO parameters.

Your “calculate_area” function takes in two items of data, and sends out one item – but it has 2 formal parameters – length and width.

“display_area” has one formal parameter.

The actual parameters are in the main program.

length, breadth = get_inputs() has no parameters.

area = calculate_area(length, breadth) has two actual parameters (length and breadth) corresponding to the formal parameters in the function (also called length and breadth).

[David Muir]

14/06/2018 at 6:42 am

I can’t add to Peter’s reply as he explains what’s what very clearly.

In terms of teaching parameter passing though, in any programming examples I show pupils, I always use different variable names for the actual parameters and the formal parameters to make it easier to refer to them when talking to the pupils. So, I might define the sub-program as –
def calculate_area(f_length, f_breadth):
and/or call the sub-program in the main program with –
area = calculate_area(l, b)

I don’t know if it helps, but the other thing I do is tell pupils:
Formal parameters in the sub-program deFinition
Actual parameters in the sub-program cAll

[Susan Thomson]

14/06/2018 at 2:05 pm

This has been a good help.

Many thanks to everyone who contributed.