Dynamic variable in function argument

Question

Let us say I have a function like this:

def helloWorld(**args):
    for arg in args:
        print(args[arg])

To call this function is easy:

helloWorld(myMsg = 'hello, world')
helloWorld(anotherMessages = 'no, no this is hard')

But the hard part is that I want to dynamically name the args from variables coming from a list or somewhere else. And I'd want for myMsg and anotherMessages to be passed from a list (for example, the hard part that I am clueless and I need help with is how to take strings into variables to be inputs of a function).

list_of_variable_names = ['myMsg','anotherMessages']
for name in list_of_variable_names:
    helloWorld(name = 'ooops, this is not easy, how do I pass a variable name that is stored as a string in a list? No idea! help!')

Moses Koledoye · Accepted Answer · 2017-07-18 13:47:27Z

3

You can create a dict using the variable and then unpack while passing it to the function:

list_of_variable_names = ['myMsg','anotherMessages']
for name in list_of_variable_names:
    helloWorld(**{name: '...'})

answered Jul 18, 2017 at 13:47

Moses Koledoye

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1 Comment

Dnaiel Over a year ago

interesting, let me try it out

Right leg · Accepted Answer · 2017-07-18 14:03:40Z

The ** syntax is a dictionary unpacking. So in your function, args (which is usually kwargs) is a dictionary.

Therefore, you need to pass an unpacked dictionary to it, which is what is done when f(a=1, b=2) is called.

For instance:

kwargs = {'myMsg': "hello, world", 'anotherMessages': "no, no this is hard"}
helloWorld(**kwargs)

Then, you will get kwargs as a dictionary.

def f(**kwargs):
    for k, v in kwargs.items():
        print(k, v)

>>> kwargs = {'a': 1, 'b': 2}
>>> f(**kwargs)
a 1
b 2

If you want to do so, you can call the function once for every name as well, by creating a dictionary on the fly and unpacking it, as Moses suggested.

def f(**kwargs):
    print("call to f")
    for k, v in kwargs.items():
        print(k, v)

>>> for k, v in {'a': 1, 'b': 2}:
...     kwargs = {k: v}
...     f(**kwargs)
...
call to f
a 1
call to f
b 2

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