Python function returning redundant values

Question

I have a python function which returns all keys and children of a Btree:

def getAllElements(self,output=[]):
        for i in self.values:
            output.append(i)
        if not self.children == None:
            for i in self.children:
                i.getAllElements(output)
        return output

I am calling this function from other multiple functions like:

all_elements1 = self.getAllElements()

When I print this from multiple functions I get redundant output, like:

def f1():
    all_elements1 = self.getAllElements()
    print(all_elements1)

def f2():
    all_elements2 = self.getAllElements()
    print(all_elements2)

def f3():
    all_elements3 = self.getAllElements()
    print(all_elements3)

I get output say as:

1
11
111

I don't understand why this is happening. I want just 1 always.