arbitrary number of arguments in a python function

Question

I'd like to learn how to pass an arbitrary number of args in a python function, so I wrote a simple sum function in a recursive way as follows:

def mySum(*args):
  if len(args) == 1:
    return args[0]
  else:
    return args[-1] + mySum(args[:-1])

but when I tested mySum(3, 4) , I got this error:

TypeError: unsupported operand type(s) for +: 'int' and 'tuple'

Does anyone have an idea about this and gimme some clue to correct it?

Answer 1

This line:

return args[-1] + mySum(args[:-1])

args[:-1] returns a slice of the arguments tuple. I assume your goal is to recursively call your function using that slice of the arguments. Unfortunately, your current code simply calls your function using a single object - the slice itself.

What you want to do instead is to call with those args unrolled.

return args[-1] + mySum(*args[:-1])
                        ^---- note the asterisk

This technique is called " unpacking argument lists ," and the asterisk is sometimes (informally) called the "splat" operator.

Answer 2

If you don't want to do it recursively:

def mySum(*args):
sum = 0
for i in args:
        sum = sum + i
return sum

Answer 3

args[:-1] is a tuple, so the nested call is actually mySum((4,)) , and the nested return of args[0] returns a tuple. So you end up with the last line being reduced to return 3 + (4,) . To fix this you need to expand the tuple when calling mySum by changing the last line to return args[-1] + mySum(*args[:-1]) .

Answer 4

In your code, args[:-1] is a tuple, so mySum(args[:-1]) is being called with the args being a tuple containing another tuple as the first argument. You want to call the function mySum with args[:-1] expanded to the arguments however, which you can do with

mySum(*args[:-1])

Answer 5

The arbitrary arguments are passed as tuple (with one asterisk*) to the function, (you can change it to a list as shown in the code) and calculate the sum of its elements, by coding yourself using a for loop; if don't want to use the sum() method of python.

def summing(*arg):
    li = list(*arg)
    x = 0
    for i in range((len(li)-1)):
        x = li[i]+x

    return x

#creating a list and pass it as arbitrary argument to the function
#to colculate the sum of it's elements

li = [4, 5 ,3, 24, 6, 67, 1]
print summing(li)

Answer 6

Option1:

def mySum(*args):
    return sum(args)

mySum(1,2,3) # 6
mySum(1,2) # 3

Option 2:

mySum2 = lambda *args: sum(args)
mySum2(1,2,3) # 6
mySum2(1,2) # 3