[1LP][RFR] Fix dangerous arg value

[jarovo]

Using mutable as default arg value is dangerous as it is evaluated once, when function is being created (module loaded).

This value is preserved between each function calls and when modified, the subsequent calls will use the new state of that default object.

In [2]: def foo(aaa=[]): 
   ...:     aaa.append(3) 
   ...:     return aaa 
   ...:                                                                                                                                                                                       

In [3]: a=foo()                                                                                                                                                                               

In [4]: a                                                                                                                                                                                     
Out[4]: [3]

In [5]: a=foo()                                                                                                                                                                               

In [6]: a                                                                                                                                                                                     
Out[6]: [3, 3]