Suppose one has several separate functions to evaluate some given data. Rather than use redundant if/else loops, one decides to use a dictionary key to find the particular function and its corresponding args. I feel like this is possible, but I can't figure out how to make this work. As a simplified example (that I hope to adapt for my case), consider the code below:
def func_one(x, a, b, c=0):
""" arbitrary function """
# c is initialized since it is necessary in func_two and has no effect in func_one
return a*x + b
def func_two(x, a, b, c):
""" arbitrary function """
return a*x**2 + b*x + c
def pick_function(key, x=5):
""" picks and evaluates arbitrary function by key """
if key != (1 or 2):
raise ValueError("key = 1 or 2")
## args = a, b, c
args_one = (1, 2, 3)
args_two = (4, 5, 3)
## function dictionary
func_dict = dict(zip([1, 2], [func_one, func_two]))
## args dictionary
args_dict = dict(zip([1, 2], [args_one, args_two]))
## apply function to args
func = func_dict[key]
args = args_dict[key]
## my original attempt >> return func(x, args)
return func(x, *args) ## << EDITED SOLUTION VIA COMMENTS BELOW
print(func_one(x=5, a=1, b=2, c=3)) # prints 7
But,
print(pick_function(1))
returns an error message
File "stack_overflow_example_question.py", line 17, in pick_function
return func(x, args)
TypeError: func_one() missing 1 required positional argument: 'b'
Clearly, not all of the args are being passed through with the dictionary. I've tried various combinations of adding/removing extra brackets and paranthesis from args_one and args_two (as defined in pick_function). Is this approach fruitful? Are there other convenient (in terms of readability and speed) approaches that do not require many if/else loops?
To fix your code with minimal changes, change return func(x, args) to return func(x, *args). I think this is what Anton vBR is suggesting in the comments.
However, I think your code could be further simplified by
using the * ("splat") and ** ("double-splat"?) positional/keyword argument unpacking operators like this:
def func_one(x, a, b, c=0):
""" arbitrary function """
# c is initialized since it is necessary in func_two and has no effect in func_one
return a*x + b
def func_two(x, a, b, c):
""" arbitrary function """
return a*x**2 + b*x + c
def func(key, *args, **kwargs):
funcmap = {1: func_one, 2: func_two}
return funcmap[key](*args, **kwargs)
def pick_function(key, x=5):
""" picks and evaluates arbitrary function by key """
argmap = {1: (1, 2, 3), 2: (4, 5, 3)}
return func(key, x, *argmap[key])
print(func_one(x=5, a=1, b=2, c=3))
# 7
print(pick_function(1))
# 7
print(func(1, 5, 1, 2, 3))
# 7
print(func(1, b=2, a=1, c=3, x=5))
# 7