How to set a python property in __init__

Question

I have a class with an attribute I wish to turn into a property, but this attribute is set within __init__. Not sure how this should be done. Without setting the property in __init__ this is easy and works well

import datetime  class STransaction(object):     """A statement transaction"""     def __init__(self):         self._date = None      @property     def date(self):         return self._date      @date.setter     def date(self, value):         d = datetime.datetime.strptime(value, "%d-%b-%y")         self._date = d  st = STransaction() st.date = "20-Jan-10" 

But once initialization needs to occur in __init__ it gets more complicated and I am not sure of the correct course of action.

class STransaction(object):     """A statement transaction"""     def __init__(self, date):         self._date = None 

Strangely to me, the following seems to work but smells very bad.

class STransaction(object):     """A statement transaction"""     def __init__(self, date):         self._date = None         self.date = date      @property     def date(self):         return self._date      @date.setter     def date(self, value):         d = datetime.datetime.strptime(value, "%d-%b-%y")         self._date = d 

What is the correct way to go about setting properties in __init__?

Thanks, Aaron.

Answer 1

I do not see any real problem with your code. In __init__, the class is fully created and thus the properties accessible.

Answer 2

class STransaction(object):     """A statement transaction"""     def __init__(self, date):         self._date = None #1         self.date = date  #2 

If you want to set the proxy field self._date without executing of your setter use the #1 line. If you would like to execute the setter at startup too use the #2. Both ways are correct, it's just a matter of what do you want to do.