reassign values to args of a function

Question

i have a function with about 20-30 parameters

def function (a,b,c,d,e,....):

     ....

those paramenters may have any value, including "None".
I want to reasign a specifique string to each var that has the value "None" before my function does its magic.

But I dont want to have a huge block of code such as:

if a is None:
     ....
if b is None: ....

How can I go through each var and reasign its value if the condition is met?

ty

Use classes to group related parameters. Delegate the `if`s to the classes. Don't write 30 parameter functions — Mad Physicist, Jun 24 '19 at 15:52
Why not simply [default argument values](https://docs.python.org/3/tutorial/controlflow.html#default-argument-values) ? — Corentin Limier, Jun 24 '19 at 15:54
If I use default parameters that arent None, wouldnt they get overwritten when I call the function with the new arguments that are None? — epattaro, Jun 24 '19 at 15:57
using a dictonary does sound simpler. also found a solution at https://stackoverflow.com/questions/582056/getting-list-of-parameter-names-inside-python-function — epattaro, Jun 24 '19 at 15:58

score 2 · Accepted Answer · answered Jun 24 '19 at 16:02

2

Unless you are doing something pretty exotic, this kind of thing is usually better handled by collecting the variables in a data structure, e.g. a dict like so:

def function(**kwargs):
    default = 42
    for key, val in kwargs.items():
        if val is None:
            kwargs[key] = default
    ...
    print(kwargs)

# Example call
function(a=1, b=None)

You can assign to individual variables using the magic of exec, but it's generally not advised. Furthermore, it's not clear to me how one can successfully use this inside of a function as e.g. exec('a = 42') doesn't actually change the value of the local a variable.

answered Jun 24 '19 at 16:02

jmd_dk

12,125
9
63
94

ty. thats what i was looking for. fyi: the function takes a bunch of strings as parameters, but what generates the strings can also produce a None element, depending on user interaction (html component). – epattaro Jun 24 '19 at 16:07
2

This assumes that the function is called with keyword arguments; if I try `function(1,None)`, it will fail. – Scott Hunter Jun 24 '19 at 16:08

Vasu Deo.S · Answer 2 · 2019-06-24T16:25:18.073

1

If you have so many arguments to the function, then you can try using iterable unpacking operator * instead of explicitly defining each argument. In that you you will have more control over the contents of the arguments:-

def function(*args):
    args = list(args)
    for x, y in enumerate(args):
        if y is None:
            args[x] = "default_value"
    print(args)

Then do a function call similar to :-

function(123, 3, None, "hello")

OUTPUT:-

[123, 3, 'default_value', 'hello']

edited Jun 24 '19 at 16:25

answered Jun 24 '19 at 15:58

Vasu Deo.S

1,820
1
11
23

This does not address *changing* parameters, just *identifying* them. – Scott Hunter Jun 24 '19 at 16:03
if I use *args can i still name my parameters? – epattaro Jun 24 '19 at 16:04
@epattaro then your parameters becomes a tuple, so you can index them off it – Vasu Deo.S Jun 24 '19 at 16:20
Thanks @ScottHunter For pointing that out. Edited the answer accordingly. – Vasu Deo.S Jun 24 '19 at 16:25
This fails if called with named arguments. – Scott Hunter Jun 24 '19 at 17:16

score 0 · Answer 3 · answered Jun 24 '19 at 16:05

0

I'm not recommending doing this, but if you insist:

def function(a,b,c,d,e,...):
    myvars = locals()         # Get a dictionary of parameters
    arg_names = myvars.keys() # Get their names
    for k in arg_names:       # Replace the ones whose value is None
        if myvars[k] == None:
            myvars[k] = 'None'

answered Jun 24 '19 at 16:05

Scott Hunter

48,888
12
60
101

that works even better. ty. i should problaby be using a dictionary as an input, or is there a better solution? – epattaro Jun 24 '19 at 16:12

reassign values to args of a function

3 Answers3