[Python-Dev] Proposal: make float.__str__ identical to float__repr__ in Python 3.2

[Raymond Hettinger]

>> When you proposed the idea at EuroPython, it seemed reasonable
>> but we didn't go into the pros and cons.  The downsides include
>> breaking tests, changing the output of report generating scripts
>> that aren't using string formatting, and it introduces another
>> inter-version incompatibility.
> 
> Yes, I agree that the change has potential for breakage;  it's a
> change that probably would have been unacceptable for Python 2.7;  for
> Python 3.2 I think there's a little more scope, since 3.x has fewer
> users.

+1 for making the change to 3.2
+0 for 2.7


>> The only obvious advantage is
>> that it makes float.__repr__ and float.__str__ the same, making
>> one less thing to explain.  Can you elaborate on other advantages?
>> Is there something wrong with the current way?
> 
> That's one advantage;  as mentioned earlier the difference between str
> and repr causes confusion for floats in containers, where users don't
> realize that two different operations are being used.  This is a
> genuine problem: I've answered questions about this a couple of times
> on the #python IRC channel.
> 
> Another advantage is that is makes 'str' faithful:  that is, if x and
> y are distinct floats then str(x) and str(y) are guaranteed distinct.
> I know I should know better, but I've been bitten by the lack of
> faithfulness a couple of times when debugging floating-point problems:
> I insert a "print(x, y)" line into the code for debugging purposes
> and still wonder why my 'assertEqual(x, y)' test is failing even
> though x and y look the same;  only then do I remember that I need to
> use repr instead.
> 
> As you say, it's just one less surprise, and one less thing to
> explain: a small shrinkage of the mental footprint of the language.

Thanks for listing the advantages.
Sounds like it is worth the cost.

It also really calls into question whether there are good
reasons for other types to have a __str__ that is different
than their __repr__.


Raymond