Constructor re-initialization issue

Michael Mabin d3vvnull at gmail.com
Wed Jun 4 01:13:42 CEST 2008


Changing the default for data to None and creating a new dict inside your
function might handle this.  But I don't know what it is you want.  It never
even occurred to me that this behavior might be desired in the first place.

class Param(object):
   def __init__(self,data=None,condition=False):
       if data is None:
          data = {}
       if condition:
          data['class'] = 'Advanced'
       print data

Param(condition=True)
Param(condition=False)

I always thought you didn't want to have empty sequences as default values.

On Tue, Jun 3, 2008 at 5:11 PM, <pythonreptile at gmail.com> wrote:

> Hello all,
>
> I have come across this issue in Python and I cannot quite understand
> what is going on.
>
> class Param():
>    def __init__(self, data={}, condition=False):
>        if condition:
>            data['class']="Advanced"
>        print data
>
> In the previous example, I expect the variable data to be re-
> initialized every time I construct an object type Param. However, when
> I do the following:
>
> Param(condition=True)
> Param(condition=False)
>
> The second call still prints {'class': 'Advanced'}
>
> Shouldn't data be initialized to {} since it is the default in
> __init__? Why would the state of data be preserved between two
> independent instantiations?
>
> Any help would be greatly appreciated.
>
> M.
> --
> http://mail.python.org/mailman/listinfo/python-list
>



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