[Python-ideas] Disallow "00000" as a synonym for "0"

Steven D'Aprano steve at pearwood.info
Mon Jul 20 04:01:55 CEST 2015

On Mon, Jul 20, 2015 at 10:38:02AM +1000, Nick Coghlan wrote:

> Exactly - the special case here is *dis*allowing leading zeroes for
> non-zero integer literals, 

That's a ... different ... definition of "special case". You're saying 
that, out of the literally infinite number of possible ints one might 
attempt to write, *all of them except zero* are the special case, while 
zero itself is the non-special case. O-kay.

I get the argument that allowing people to write 000000000 when they 
want a int zero is harmless, and the code churn required to prevent that 
outweighs any benefit gained. The task I created on the tracker has been 
closed as a "won't fix" or "rejected" (I forget which one), and I'm not 
going to argue with that. But I did find your perspective above funny 
enough that I had to reply.

But for the record, and this will be my last word on the subject:

> since we can't know if they're supposed to be
> octal values or not, or if the "b" or "x" was left out of a binary or hex
> literal that has been padded out to a fixed number of bits, or if the
> decimal point was left out of a floating point literal.

Right. So if you see somebody has written 00 as a literal in Python 3, 
it's *more likely to be an error than deliberate*. E.g. we can align 
octal or hex numbers using a fixed width string with leading zeroes 
where needed:

nums = [0x00001234,
        0x00000000,  # this is okay
        00000000,  # breaks the alignment
        0000000000,  # aligned but where's the X?

but if you see a plain, unprefixed 0 mixed in there, that smells of an 
possible error. Even if it isn't an error, to me it hints of an error 
enough that I'd want to question the code author's intention. "Did you 
really mean zero, or is that a typo?"

Regardless of everything else, to me this is an aesthetic question. 
Allowing 00 when 01, 02, 03, ... are (rightly!) forbidden feels ugly and 
a wart. But until and unless somebody actually gets bitten by this in 
real code, and a typo hides in plain view disguised as zero, I can't 
honestly say it is outrightly harmful.


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