eval(repr(x)) == x

[Alex Martelli]

Oren Tirosh wrote:

> For many python builtins eval(repr(x)) == x.  I find this property very
> useful for debugging and writing tests.  In some cases I write my own
> classes so their repr is an expression that recreates their state.

It's sort of nice when it works, but I don't quite see how this translates
into "very useful for debugging and writing tests".  Examples please?


> For some python builtins this could be true, but isn't.  Is there anyone
> else who thinks it might be more consistent if this applied to more
> builtins?  I'm mostly talking about objects that have a __name__ attribute
> like types, classes and functions.
> 
> The __repr__ function for these types could be something like this:
>  
>   def __repr__(self):
>     return "%s.%s" % (self.__module__, self.__name__)

I would find it somewhat of a problem not being able to tell from repr(x) 
whether x is a function, a submodule of a package, a class, etc.  I think
it's more important for repr(x) to identify x reasonably well (compatibly
with not taking up a thousand characters:-) rather than striving for repr
to be eval's inverse -- which it can be only up to a point (e.g. the above
repr only works after
        import module
and not after
        from module import function
and the like).


Alex