Python Forum

I have the following question regarding using parenthesis when calling use defined function.

This is the code proposed by the book to simulate white noise process for 100 periods using User-Defined Function.

def generate_data(n, generator_type):
    ϵ_values = []
    for i in range(n):
        e = generator_type()
        ϵ_values.append(e)
    return ϵ_values

data = generate_data(100, np.random.uniform)
plt.plot(data)
plt.show()

I am trying to change this code in the following way:

def generate_data(n, generator_type):
    ϵ_values = []
    for i in range(n):
        e = generator_type
        ϵ_values.append(e)
    return ϵ_values

data = generate_data(100, np.random.uniform())
plt.plot(data)
plt.show()

So, instead of having parenthesis inside the body of the function (e=generator_type()) I provide it as the name of the second variable in the function generate_data. But the code does not run in the second case. I wonder what is the difference and why it fails to provide the same results as the first version. The call should just take np.random.uniform() instead of generator_type and produce the same result should not it? Why should I put generator_type() parenthesis in the body and then put np.random.uniform as the variable? why does it make a difference where to put ()?

The difference is that in the first case the function generator_type() is called for every index in the loop for i in ramge... while in the second case it is called only once.

data = generate_data(100, np.random.uniform)

Here the function np.random.uniform is given as a parameter to the function
and inside the function the according argument name generator_type can be used to call the function by adding ()

data = generate_data(100, np.random.uniform())

Here you are CALLING the function np.random.uniform once and that call returns a random value
and that value is passed as a parameter to the function and then assigned to e and then to the ϵ_values list.
So your 2nd code snippet runs but all values are the same.