property question

[Markus Jais]

Chris Liechti wrote:

> Markus Jais <info at mjais.de> wrote in
> news:acjnug$q6c68$1 at ID-75083.news.dfncis.de:
> 
>> hello
>> 
>> Just started playing with python 2.2 and the new features.
>> Now I have a question on properties:
>> 
>> class Address(object):
>> 
>>         def __init__(self):
>>                 self.firstname     = ""
>>                 self.lastname      = ""
>>                 self.email         = ""
>> 
>>         def set_email(self, email):
>>                 print "in set email"
>>                 self.email = email
>> 
>>         def get_email(self):
>>                 print "in get mail"
>>                 return "<" + self.email + ">"
>>         
>>         email = property(get_email, set_email, None, 'Setting the
>>         email adress')
>> 
>> if __name__ == '__main__':
>>         print "testing"
>> 
>>         a = Address()
>>         a.firstname = "gandalf"
>>         a.email = "wizard at middle-earth.com"
>>         print a.firstname
>>         print a.email
>> 
>> 
>> I get an endless recustion because I refer to self.email in the get_
>> and set_ method
>> 
>> how can I set the value of self.email and how can I return a modified
>> version in the get method??
> 
> i think the usual way is to store the value in a variable with preceeding
> underlines ("self._email" or two underlines if you want a private
> attribute)

thanks for your tip: using an underline works
but when I use two underlines with slots like this

class Address(object):

        __slots__ = ('firstname', 'lastname', __email')

        def __init__(self):
                self.firstname     = ""
                self.lastname      = ""
                self.__email         = "
        def set_email(self, email):
                print "in set email"
                self.__email = email

......

I get this error:

Traceback (most recent call last):
  File "./Address.py", line 49, in ?
    a = Address()
  File "./Address.py", line 24, in __init__
    self.__email         = ""
AttributeError: 'Address' object has no attribute '_Address__email'


but with one underline, it works just fine.

markus