Python passing list as argument

Question

If i were to run this code:

def function(y):     y.append('yes')     return y  example = list() function(example) print(example) 

Why would it return ['yes'] even though i am not directly changing the variable 'example', and how could I modify the code so that 'example' is not effected by the function?

Answer 1

Everything is a reference in Python. If you wish to avoid that behavior you would have to create a new copy of the original with list(). If the list contains more references, you'd need to use deepcopy()

def modify(l):  l.append('HI')  return l  def preserve(l):  t = list(l)  t.append('HI')  return t  example = list() modify(example) print(example)  example = list() preserve(example) print(example) 

outputs

['HI'] []