[Python-ideas] automation of repr/str for all the common simple cases

Thu Feb 16 00:43:33 CET 2012

Ronny Pfannschmidt wrote:
> Hi,
>> in my experience for many cases, __repr__ and __str__ can be 
> unconditionally be represented as simple string formatting operation,

In my experience, not so much.
> so i would propose to add a extension to support simply declaring them 
> in the form of newstyle format strings

Declare them how? What is your proposed API for using this new functionality? 
Before proposing an implementation, you should propose an interface.
> a basic implementation for __repr__ could look like:
>> class SelfFormatter(string.Formatter):
> def __init__(self, obj):
> self.__obj = obj
> string.Formatter.__init__(self)
>> def get_value(self, key, args, kwargs):
> if isinstance(key, str) and hasattr(self.__obj, key):
> return getattr(self.__obj, key)
> return Formatter.get_value(self, key, args, kwargs)
>> class SimpleReprMixing(object):
> _repr_ = '<{__class__.__name__} at 0x{__id__!x}>'
> def __repr__(self):
> formatter = SelfFormatter(self)
> return formatter.vformat(self._repr_, (), {'__id__':id(self)})

I don't think you need this just to get a generic "instance at id" string. If 
you inherit from object (and remember that all classes inherit from object in 
Python 3) you get this for free:
 >>> class K(object):
... pass
...
 >>> k = K()
 >>> str(k)
'<__main__.K object at 0xb746068c>'
-- 
Steven

[Python-ideas] automation of __repr__/__str__ for all the common simple cases

[Python-ideas] automation of repr/str for all the common simple cases