ufl team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Monday May 2 2011 14:37:23 Anders Logg wrote:
> On Mon, May 02, 2011 at 02:02:02PM -0700, Johan Hake wrote:
> > Run this and see whats happens:
> > 
> > def jada(bada=[]):
> >     bada.append(5)
> >     return bada
> > 
> > print jada()
> > print jada()
> 
> Cool. I didn't know. Looks like a good feature that could be used to
> write some obfuscated Python code. :-)

Hold your horses!

Johan

> --
> Anders
> 
> > Johan
> > 
> > On Monday May 2 2011 13:55:53 Anders Logg wrote:
> > > On Mon, May 02, 2011 at 01:26:58PM +0200, Martin Sandve Alnæs wrote:
> > > > Declaring default arguments with mutable object like dicts such as
> > > > this line is dangerous in Python.
> > > > def compute_form_data(self, object_names={}, common_cell=None,
> > > > element_mapping={}):
> > > > If object_names or element_mapping is modified, the
> > > > modifications change the default object for future calls.
> > > 
> > > How do you mean modified? You mean the default will change if a value
> > > is passed to the function with element_mapping=<something>?
> > > 
> > > > Therefore it's a good habit to use None instead:
> > > > def compute_form_data(self, object_names=None, common_cell=None,
> > > > 
> > > > element_mapping=None):
> > > >     if object_names is None: object_names = {}
> > > >     if element_mapping is None: element_mapping = {}
> > > >     ...
> > > 
> > > ok.