run a string as code?

[py_genetic]

Gary Herron wrote:
> py_genetic wrote:
> > py_genetic wrote:
> >
> >> mtbeedee at gmail.com wrote:
> >>
> >>> py_genetic wrote:
> >>>
> >>>> How can you make python interpret a string (of py code) as code.  For
> >>>> example if you want a py program to modify itself as it runs.  I know
> >>>> this is an advantage of interpreted languages, how is this done in
> >>>> python.  Thanks.
> >>>>
> >>> This might do it...
> >>>
> >>>
> >>>>>> print eval.__doc__
> >>>>>>
> >>> eval(source[, globals[, locals]]) -> value
> >>>
> >>> Evaluate the source in the context of globals and locals.
> >>> The source may be a string representing a Python expression
> >>> or a code object as returned by compile().
> >>> The globals must be a dictionary and locals can be any mappping,
> >>> defaulting to the current globals and locals.
> >>> If only globals is given, locals defaults to it.
> >>>
> >> For example each time this line is interpreted I would like to use the
> >> new value of the state var which is a global var.  How can I force
> >> state to be identified and used in this string.
> >>
> >> r_table = h5file.root.state_raw_records.neg_records
> >>
> >> r_table = eval("h5file.root.state_raw_records.neg_records") ??
> >> r_table = h5file.root.eval("state")_raw_records.neg_records ?? eval is
> >> not a part of root
> >>
> >> dont think either of these is very logical? Any ideas?  Possibly the
> >> parser mod?
> >>
> >
> > Got it!
> >
> > tmp = "h5file.root."+state+"_raw_records.pos_records"
> > r_table = eval(tmp)
> >
> > works great thanks for the help!
> >
> Yes, it works, but this is not a good place to use eval. Now that we see
> how you want to use it, we can find a *much* better way to do it.
>
> If you want to lookup an attribute of an object, but the attribute name
> is a string in a variable, then use getattr to do the lookup.
>
> If in interpret your code correctly:
>
> attrname = state + "_raw_records"
> obj = getattr(h5file.root, attrname)
> r_table = obj.pos_records
>
> These, of course, could be combined into a single (but not necessarily
> clearer) line.
>
> Gary Herron

So it is eval() is more appropriate when evalution blocks of string
code, and getattr() is more efficient for dealing with objects such as
h5file object above?  Thanks.