Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #29561

Re: Fool Python class with imaginary members (serious guru stuff inside)

Show all headers | View raw

On 9/20/2012 9:52 AM, Jure Erznožnik wrote:
> I'm trying to create a class that would lie to the user that a member is in some cases a simple variable and in other cases a class. The nature of the member would depend on call syntax like so:
> 1. x = obj.member #x becomes the "simple" value contained in member
> 2. x = obj.member.another_member #x becomes the "simple" value contained in first member's another_member.

x.y.z is parsed and executed as (x.y).z, so you are asking if the 
attribute-getter can know what will be done with the object it returns.
Assuming CPython, you would have to write something that searches the 
Python code before compilation, the ast during compilation, or the 
bytecode after compilation.

Much easier would be to define a union class that is a simple type with 
attributes and return that in the first lookup.

class AttrInt(int):
     def __getattr__(self, name): return 'attribute'

y = AttrInt(3)
print(y, y.a)
###
3 attribute

If x.y returns an AttrInt, it will act like an int for most purposes, 
while x.y.z will return whatever AttrInt.__getattr__ does and the 
temporary AttrInt y disappears.

-- 
Terry Jan Reedy

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Fool Python class with imaginary members (serious guru stuff inside) Jure Erznožnik <jure.erznoznik@gmail.com> - 2012-09-20 06:52 -0700
  Re: Fool Python class with imaginary members (serious guru stuff inside) Terry Reedy <tjreedy@udel.edu> - 2012-09-20 13:04 -0400
  Re: Fool Python class with imaginary members (serious guru stuff inside) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-20 19:15 +0000

csiph-web