Python passing list as argument [duplicate]

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']
[]