__repr__ policy problem: should module be prefixed to output?

Pearu Peterson pearu at cens.ioc.ee
Fri Dec 15 20:54:58 CET 2000


On Fri, 15 Dec 2000, Alex Martelli wrote:

> "Per Kraulis" <per at sbc.su.se> wrote in message
> news:3A3A3A6D.2C3B1A91 at sbc.su.se...

> > The problem is that Alt 1 is appropriate in the context of "import
> > crng", while Alt 2 is better when having done "from crng import *".
> 
> If it was only the latter, it would not be worth supporting except
> for those very rare modules that are _designed_ to be from-import-*'ed.
> 
> But a more reasonable usage, such as:
> 
>     from themodule import specificthing, anothergoodie, classname
> 
> would also favour repr strings of the form 'classname(avalue)' over
> 'themodule.classname(avalue)'.
> 
> Existing modules seem to do it both ways, so it's hard to
> find specific precedents for guidance.
> 
> One thing favouring the 'undecorated' form is that an eval
> _using the module's dictionary as global-dictionary_ should
> then work anyway (as well as string-manipulations before
> eval, which are of course possible in either case).
> 

There is a solution to this repr string dilemma. For example,
consider foo.py:

# begin of file foo.py
class A:
    def __init__(self,value):
        self.value = value
    def __repr__(self):
        return '%s.%s(%s)'%(self.__module__,
                            self.__class__.__name__,
                            self.value)

exec 'import %s'%__name__   # this does the trick
                            # (could it be done also in C extension
                            #  modules?)

#eof foo.py

Now in python session:

>>> import foo
>>> foo.A(3)
foo.A(3)
>>> eval(repr(foo.A(3)))
foo.A(3)

and in another python session:

>>> from foo import *
>>> A(3)
foo.A(3)
>>> eval(repr(A(3)))
foo.A(3)

And the answer to the original question is Yes.

Regards,
	Pearu




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