Is there a way to extract function parameters from a dictionary? - python-3.x

Question

I am trying to create some more functional code in Python and I want to know if it is possible to transform dictionary (key,values) to pass as a function parameter.
I am currently doing this in a more imperative way, where I filter and then manually extract each key depending on the result of the filter. My current code:
def a(i: int, config: dict):
function_array = [function1, function2, function3]
selected = function_array[i]
if (i == "0"):
result = selected(x = config['x'])
elif (i == "1"):
result = selected(y = config['y'])
elif (i == "2"):
result = selected(z = config['z'])
return result
The current result is correct, but when I have many cases, I need to hardcode each parameter for the specified function. So, that is why I want to know if it is possible to pass the config object as I want (with an x when i is 0, for example) and then just do something like this:
def a(i: int, config: dict):
function_array = [function1, function2, function3]
result = function_array[i](config)
return result

Answer 1

The syntax for passing items from a dictionary as function parameters is simply selected(**config)
So for your example, it would look something like this:
def function1(x=0):
return x + 1
def function2(y=42):
return y * 2
def function3(z=100):
return z
def a(i, config):
function_array = [function1, function2, function3]
selected = function_array[i]
return selected(**config)
config = {x: 10}
a(0, config) # calls function1(x=10)
config = {y: 20}
a(1, config) # calls function2(y=20)
config = {}
a(2, config) # calls function3()

Answer 2

Every python function can be instructed to take a dictionary of keywords. See e.g. https://www.pythoncheatsheet.org/blog/python-easy-args-kwargs . (Official source at https://docs.python.org/3/reference/compound_stmts.html#function-definitions, but it's harder to read.)
You could do:
def a(i: int, keyword: str, **kwargs: dict):
if keyword in kwargs:
result = kwargs[keyword](i)
and you would run it with something like:
a(5, "func3", func1=print, func2=sum, func3=all)
Or, you could just pass a dictionary itself into the function:
def a(i: int, keyword: str, config: dict)
if keyword in config:
result = config[keyword](i)
This would be run with something like:
a(5, "func3", {"func1": print, "func2": sum, "func3": all})
The only difference is that the ** in the function declaration tells python to automatically make a dictionary out of explicit keywords. In the second example, you make the dictionary by yourself.
There's an important thing happening behind the scenes here. Functions are being passed around just like anything else. In python, functions are still objects. You can pass a function just as easily as you can pass an int. So if you wanted to have a list of lists, where each inner list is a function with some arguments, you easily could:
things_to_do = [[sum, 5, 7, 9], [any, 1, 0], [all, 1, 0]]
for thing_list in things_to_do:
function = thing_list[0]
args = thing_list[1:]
print(function(args))
And you'll get the following results:
21
True
False
(Note also that all of those functions take an iterable, such as a list. If you want to pass each argument separately, you would use *args instead of args.)
You can do it with defined functions, too. If you have
def foo1(arg1):
pass
def foo2(arg1, arg2):
pass
you can just as easily have
things_to_do = [[sum, 5, 7, 9], [foo1, 'a'], [foo2, 0, None]]