Why do the calls to name_exists and email_exists not need parentheses?

Question

Why the calls to the custom validators 'name_exists' and 'email_exists' not need parentheses?

Especially confusing as the Flask provided validators such as DataRequired does need the parentheses.

Answer 1 · 2020-11-23T20:42:54Z

November 23, 2020 8:42pm

The validator is taking in the function as an object reference rather than results. It's sort of a generic way that you can pass a function as an object.

Recall that Python functions are "first class citizens" just like all other objects. In this case, those functions are being passed as objects to the validator. And we can also get a variable number of arguments *args or keyword arguments **kwargs` see example below...

def generic_function_executor(my_function, *args, **kwargs):
    """Here is a generic function executor which will execute ANY function object"""
    result = my_function(*args, **kwargs)
    return result

def add(x,y):
    """Here is a simple add function of two variables"""
    return x+y

def mult(x,y):
    """This is a simple multiplier of two variables"""
    return x*y

def greet(name):
    """This function just prints hello name! to the console"""
    print("Hello {}!".format(name))

# now, we can execute these functions with a single argument or an argument list.
print( generic_function_executor(add, 2, 3) )
print( generic_function_executor(mult, 2, 3) )

generic_function_executor(greet, "Pythoneer")

results in this output

5
6
Hello Pythoneer!

Welcome to the Treehouse Community

Looking to learn something new?

dodders

dodders

Why do the calls to name_exists and email_exists not need parentheses?

1 Answer

Jeff Muday

Jeff Muday