Default parameters in Python

defExtendlist (Val, test=[]): Test.append (val)returnTestlist1= Extendlist (10) List2= Extendlist (123, []) List3= Extendlist ('a')Print("List1 =%s"%List1)Print("List2 =%s"%list2)Print("list3 =%s"% list3)
Operation Result:
List1 = [Ten, ' a ']
List2 = [123]
LIST3 = [Ten, ' a ']

As the above code runs the result, when I began to learn python, I would also think that List1 should output a 10,list3, but it is not, in a method default parameter is test=[], when the method is called, when there is no value for its passing time, As List1 and List3 show, the test in both of the methods they invoke corresponds to the list in the same address space, so the output will be so.

We can avoid this problem by the following ways:

def Extendlist (Val, test=None):    if test = = None        := []    Test.append (val)    return test

Default parameters in Python