python：可选 arguments

Question

I would like to obtain a function that works like this:

operations(a, b) = a + b
operations(a, b, operation = 'subtraction') = a - b
operations(a, b, operation = 'multiplication') = a * b
operations(a, b, operation = 'division') = a / b

Operation should be an optional argument that specifies the operation to be performed. By default, it should consider the addition operation.

I was not able to achieve this using *args and **kwargs, probably because I didn't actually get how they work.

Thank you

Edit: Sorry I was making a stupid mistake. Thanks anyway.

Answer 1

You just need to provide a default value for the parameter.

def operations(a, b, operation='addition'):
    ...

---

*args lets you collect arbitrary positional arguments in a single tuple named args .

def foo(*args):
    print(args)

>>> foo(1, 2)
(1, 2)

**kwargs works the same, but for keyword arguments, collecting them in a dict :

def foo(**kwargs):
    print(kwargs)

>>> foo(a=1, b=2)
{'a': 1, 'b': 2}

**kwargs is typically used when you just need to pass an unknown set of arguments on to another function call. In your case here, you know that an argument named operation is to be used, so you can specify it by name in the parameter list.

---

You can also require that it be passed as a keyword argument, like so:

def operations(a, b, *, operation='addition'):
    ...

Now operations(a, b, 'subtraction') is illegal; it must be called like operations(a, b) or operations(a, b, operation='subtraction') .

Answer 2

you can use optional arguments:

def operation(a, b, tp = "addition"):
    if tp == "subtraction":
        return a - b
    if tp == "division":
        return a / b
    if tp == "multiplication":
        return a * b
    return a + b

print(operation(10, 20) == 30)
print(operation(10, 20, "subtraction") == -10)