[Python-ideas] fixing mutable default argument values

[Joel Bender]

Calvin Spealman wrote:

> I dont understand how that would be different than doing
> 
>   c = c if c is not None else Bar([2,3,4])
> 

Because that would be calling Bar(), perhaps creating a new Bar object, 
every time foo() is called with None for c, which is not what a default 
argument values are about.  I'm proposing a way to create function local 
singleton objects, removing them from the parameter list.

     def foo(x):
         local history = []
         history.append(x)

Rather than:

     def foo(x, history=[]):
         history.append(x)

and then hoping that nobody calls foo() with a history parameter.


Joel