Issue 985094: getattr(object,name) accepts only strings (original) (raw)

Issue985094

Created on 2004-07-04 23:21 by complex, last changed 2022-04-11 14:56 by admin. This issue is now closed.

Messages (3)
msg54188 - (view)	Author: Viktor Ferenczi (complex)	Date: 2004-07-04 23:21
getattr(object,name) function accepts only strings. This behavior prohibits some interesting usage of callables as names in database column and field references. For example: Someone references a database field: value=record.field_name Programmatically, when name is the name of the field: value=getattr(record,field_name) Calculated fields could be implemented by passing a callable as a field name: def fn(record): return '%s (%s)'%(record.name,record.number) value=getattr(record,fn) The database backend checks if the name is callable and then call the name with the record. But this cannot be implemented in the simple way if getattr checks if the name is a string or not. This is an unneccessary check in getattr, setattr and delattr, since prevents interesting solutions. Temporary workaround: value=record.__getattr__(fn) There can be many unneccessary type checks and limitations in core and library functions. They should be removed to allow free usage.
msg54189 - (view)	Author: Armin Rigo (arigo) *	Date: 2004-12-23 22:55
Logged In: YES user_id=4771 This is in part due to historical reasons. I guess you know about "property"? This is exactly what database people usually call calculated fields.
msg54190 - (view)	Author: Viktor Ferenczi (complex)	Date: 2005-01-02 00:29
Logged In: YES user_id=142612 Thanks for your comment. I know about property, of course. I had to change an old application where reimplementing everything with properties could be dificult. The problem has been solved for now. I use SQLObject (www.sqlobject.org) for new applications, whereever possible. Usage of other Object-Relational mappings (or even ZODB) are under consideration. - Viktor