Python function pointer with different arguments

Question

I have defined three functions.

def evaluate1(a, b):
    pass

def evaluate2(a, b):
    pass

def evaluate3(a, b, c):
    pass

What I want to do use a pointer to record which evaluate function I will use depending on the test inputs. The logic is as shown follows:

def test(a, b, c, d):
    # let evaluate_function records which evaluate function I will use
    if c > 1:
        evaluate_function = evaluate3 # not sure
    else:
       if d:
           evaluate_function = evaluate1
       else:
           evaluate_function = evaluate2

    # execute the evaluate function
    evaluate_function(a, b, ?)

However, since evaluate3 has different arguments from evaluate1 and evaluate3. How should I do? Thanks!

Must they have different arguments? If yes, could you use e.g. functools.partial or a lambda to wrap the one that takes three arguments such that the resulting evaluate_function always takes two arguments? If no, it would be easier if they didn't. — jonrsharpe
– jonrsharpe, Commented Apr 4, 2019 at 7:31
You can use default param in function declaration in c of evaluate3 if it can — waynelpu
– waynelpu, Commented Apr 4, 2019 at 7:33

quamrana · Accepted Answer · 2019-04-04 07:34:09Z

You have come up with a good idea of using a 'function pointer' to select the function. But since you know which function you are selecting at the time, you could also bind up the params:

def test(a, b, c, d):
    # let evaluate_function records which evaluate function I will use
    if c > 1:
        evaluate_function = evaluate3 # not sure
        params = a,b,d
    else:
       if d:
           evaluate_function = evaluate1
           params = a,b
       else:
           evaluate_function = evaluate2
           params = a,c

    # execute the evaluate function
    evaluate_function(*params)

I'll leave it to you to properly select the params.

Devesh Kumar Singh · Accepted Answer · 2019-04-04 07:41:05Z

Why not just call the evaluate functions directly instead of assigning them to a function as so. Makes it more readable

def evaluate1(a, b):
    print('evaluate1')

def evaluate2(a, b):
    print('evaluate2')

def evaluate3(a, b, c):
    print('evaluate3')

def test(a, b, c=None, d=None):
    # let evaluate_function records which evaluate function I will use
    if c and c > 1:
        evaluate3(a, b, c)
    else:
       if d:
           evaluate1(a, b)
       else:
           evaluate2(a, c)

test(1,2,c=0.1,d=1)
#evaluate1
test(1,2)
#evaluate2
test(1,2,3)
#evaluate3

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