Please, can somebody explain to me why this prints a list with both 1 & 2 in it instead of just 1in the list?

Question

def e(x, list = []):
list.append(x)
return(list)
Y = e(1)
Z = e(2)
print(Y)

Answer 1

Because each of the function calls changes the default parameter "list" of the function. It's always the same list that the numbers are appended to, so with each function call, the list is changed. Normally, you could prevent that by explicitly turning the default parameter into a new list in the function:

def e(x, list_ = []):
list_ = list(list_)
list_.append(x)
return(list_)
Y = e(1)
Z = e(2)
print(Y) #[1]

However that won't work if your list has the name "list". That's another reason why "list" should never be used as a variable name

Answer 2

Thanks Anna