What is the purpose of the lambda function in this function and what is the advantage of using it? [duplicate]

Question

I have this interesting piece of code:

def get_unit_sigmoid_func(alpha: float) -> Callable[[float], float]:
    return lambda x, alpha=alpha: 1. / (1 + (1 / np.where(x == 0, 0.01, x) - 1) ** alpha)

I just don't understand what the point of this is. Why wouldn't they write something like:

def get_unit_sigmoid_func(alpha,x):
    return 1 / (1+(1/np.where(x==0,0.01,x)-1)**alpha)

Is there any advantage to the way it's written in the first way?

Answer 1

The function

def get_unit_sigmoid_func(alpha: float) -> Callable[[float], float]:
    return lambda x, alpha=alpha: 1. / (1 + (1 / np.where(x == 0, 0.01, x) - 1) ** alpha)

returns a function that accepts a float value and an alpha. This function sets a default alpha value, so you don't need to specify it. This is useful when you need a function with a specific signature (e.g., takes one argument), but there are some parameters you want to set first (like alpha).

The function

def get_unit_sigmoid_func(alpha,x):
    return 1 / (1+(1/np.where(x==0,0.01,x)-1)**alpha)

returns the value, but notice that it takes an alpha parameter and a float.