Local variables persist in functions?

[robert]

120psi at gmail.com wrote:
> I'm a bit baffled.  Here is a bit of fairly straightforward code:
> 
> def _chunkify( l, chunkSize, _curList = list() ):
>     print _curList   # yay for printf debugging
>     if len( l ) <= chunkSize:
>         _curList.append( l )
>     else:
>         newChunk = l[:chunkSize]
>         _curList.append( newChunk )
>         _chunkify( l[chunkSize:], chunkSize, _curList )
>     return _curList
> 
> _chunkify simply breaks a sequence into a sequence of smaller lists of
> size <= chunkSize.  The first call works fine, but if I call it
> multiple times, weirdness happens.
> 
> chunks = _chunkify( list, size )   # _curList keeps its previous value!
> chunks = _chunkify( list, size, list() )    # this works as expected
> 
> Considering the default value of _curList, these statements should be
> identical.  Any pointers?  Did I miss something in the python reference
> manual?  (running 2.4.3, fyi)
> 

the default list() is only created once when the function is defined. And its later its always the same list
Use

def _chunkify( l, chunkSize, _curList=None ):
    _curList = _curList or []
    ...

then it works.

Robert