基于变量调用两个不同函数之一

Question

I have two different functions cd_0 and cd_90 which return a floating point variable. I am using curve_fit function in which I call either one of these function. I want to call either one of these functions using an var value ( cd_<var> ) which can be either 0 or 90. The var value is known at the beginning of the program and does not get modified. This being the case, I do not want to introduce a if check since it will slow down the optimization function calling these either of two functions. How to achieve this?

Answer 1

cd_func = cd_0 if var == 0 else cd_90

Later, when you want to call the chosen function:

my_float = cd_func()

Note that a dict will also solve the problem, but you still make a check on every reference. It's faster than your original if , but slower than the direct reference of cd_func .

Answer 2

While not too elegant, you can actually use a dictionary for this.

methods = {'cd_0': cd_0, 'cd_90', cd_90}

method_name = f'cd_{var}' # use f-strings since you know var

# to call
methods[method_name]()

Answer 3

There are multiple approaches to this that you can try, I will list some that are on the top of my head and choose what suits you.

1. Using python's eval function.

Python's eval would run a string as Python syntax. Example: eval("cd_{}({})".format(val, param)) which would translate to running cd_90(param) if var is 90 .

2. Using pointers to functions with an if statement.

func = cd_90 if var else cd_0

then now func is now a substitute for cd_90 or cd_0

I would advise using the 2nd solution as you don't want to call functions using eval for security concerns.

3. Assigning the functions to values of a dict object, refer to this answer.