Python complaints

[Jesse D. Sightler]

Michael Hudson wrote:
> 
> wware-nospam at world.std.com (Will Ware) writes:
> 
> > Will Ware wrote:
> > > I find myself grumbling about having to type "x = x + 1". The really
> > > clean thing to do, given that integers are objects, would be to define
> > > increment and decrement methods, so you'd type something like "i.incr()".
> >
> > Jesse D. Sightler (jsight at mindspring.com) wrote:
> > > Wouldn't this be impossible, since Integers are also immutable?  So, eg,
> > > i.incr() could only return an incremented version of i, but not actually
> > > increment i?
> >
> > Right, this is what Gordon was pointing out. A "++" method could not
> > magically reach out of its object, find the "i" variable, and bind it
> > to the incremented value.
> 
> Hate to be awkward, but when it comes to things like this, there's
> very little like this that can't be done in Python!
> 
> >>> def incr(var):
>         try:
>                 raise 1/0
>         except ZeroDivisionError:
>                 import sys,dis
>                 f = sys.exc_traceback.tb_frame.f_back
>                 loadins = f.f_code.co_code[f.f_lasti - 3:f.f_lasti]
>                 loadop = ord(loadins[0])
>                 name = dis.opname[loadop]
>                 loadarg = ord(loadins[1]) + 256*ord(loadins[2])
>                 vname = f.f_code.co_names[loadarg]
>                 f.f_locals[vname] = f.f_locals[vname] + 1
> 
> 
> >>> x=1
> >>> incr(x)
> >>> x
> 2

Ack, and I though Perl was the only language that made you do stuff like
that.  :)  Could you please explain this little piece of code?

It sure looks like byte-code dependant, self-modifying crazyness to me. 
:)

---------------
Jesse D. Sightler
http://www.biddin.com/delorean/