How can namedtuples be extended or subclassed with many additional @properties ?
For a few, one can just write the text below; but there are many,
so I'm looking for a generator or property factory.
One way would be to generate text from _fields
and exec it;
another would be an add_fields with the same effect at runtime.
(My @props are to get rows and fields
in a database scattered across several tables,
so that rec.pname
is persontable[rec.personid].pname
;
but namedtuples-with-smart-fields would have other uses too.)
""" extend namedtuple with many @properties ? """
from collections import namedtuple
Person = namedtuple( "Person", "pname paddr" ) # ...
persontable = [
Person( "Smith", "NY" ),
Person( "Jones", "IL" )
]
class Top( namedtuple( "Top_", "topid amount personid" )):
""" @property
.person -> persontable[personid]
.pname -> person.pname ...
"""
__slots__ = ()
@property
def person(self):
return persontable[self.personid]
# def add_fields( self, Top.person, Person._fields ) with the same effect as these ?
@property
def pname(self):
return self.person.pname
@property
def paddr(self):
return self.person.paddr
# ... many more
rec = Top( 0, 42, 1 )
print rec.person, rec.pname, rec.paddr
The answer to your question
is: exactly the way you're doing it! What error are you getting? To see a simpler case,
How about this?
Here's one approach, a little language: turn this into Python text like the above, and exec it.
(Expanding text-to-text is easy to do, and easy to test — you can look at the intermediate text.)
I'm sure there are similar if not-so-little such, links please ?