Trouble creating loops

[Den]

I am trying to figure out what's wrong with the code. It's supposed to be a function that counts how many times the sum of some string's elements are equal to an input number. No other libraries are supposed to be used.
For example:
string='1,2,3'
number=3

Output:
2

def calculate(string, number):
    string=''
    result=0
    new_list=[]
    new_list=[int(x) for x in string.split(',')]
    for i in range(0, len(new_list)+1,-1): 
            sum(new_list)
            if sum(new_list)==number: 
                result+= 1    
            else:
                continue
            i+=1   
    return result

Error:
ValueError: invalid literal for int() with base 10: ''