2 ms·

The problem is that the default argument is mutable. def f(a=[]): a.append('v') print a f(['ok']) # ['ok', 'v'] f() # ['v'] f() #

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']