[throwaway91919]

Can you (or someone) clarify what problem you're talking about? This seems to work as expected for me:

    def foo(x=[]):
        sum = 0
        for a in x: sum += a
        return sum
    print foo([3,5])  # 8
    print foo(x=[3]) # 3
    print foo([]) # 0
    print foo() # 0

Is it the fact that kwargs are required to have defaults? Or what?

[saltylicorice]

The problem is that the default argument is mutable.

  def f(a=[]):
    a.append('v')
    print a

  f(['ok']) # ['ok', 'v']
  f()       # ['v']
  f()       # ['v', 'v']

[throwaway91919]

Ah, thanks.

[raverbashing]

Nah, do it like this

def foo(i,x=[]):

    x.append(i)
    
    return x

foo(1)

foo(2)

See what happens