Question

I’m trying to construct a decorator in Python where I add a variable at the decoration stage. I know how to write a decorator where I simply run a function on the results of another function, but I’m having trouble with the syntax of adding an additional variable. Essentially, I want to take this dot product function:

def dot(x,y):
    temp1=[]
    for i in range(len(x)):
        temp1.append(float(x[i])*y[i])
    tempdot=sum(temp1)
    return tempdot 

and subtract the value ‘b’ from the result, all in one larger function given parameters x,y,b

Am I trying to misuse the decoration functionality in this case? Thanks.

Answer 1

import functools

def subtracter(b):
    def wrapped(func):
        @functools.wraps(func)
        def decorated_func(*args, **kwargs):
            return func(*args, **kwargs) - b
        return decorated_func
    return wrapped

Then use it as

@subtracter(b=5)
def dot(x,y):
    temp1=[]
    for i in range(len(x)):
        temp1.append(float(x[i])*y[i])
    tempdot=sum(temp1)
    return tempdot

By the way your dot function can be shorted with a generator expression like so:

def dot(x, y):
    return sum(float(x)*y for x, y in zip(x, y))