[Tutor] Why does 01 give a syntax error, but 00 (or 00...0) does not?

[Ben Finney]

boB Stepp <robertvstepp at gmail.com> writes:

> >>> 01
>   File "<stdin>", line 1
>     01
>      ^
> SyntaxError: invalid token

As you later explain, this is because in Python 3 the obsolete “leading
0 for octal notation” is invalid syntax. (Superseded by “leading ‘0o’ for
octal notation”).

> >>> 00
> 0
> >>> -00
> 0
> >>> 000
> 0
>
> Why do zeros not give a syntax error, but other numbers with a leading
> zero do give a syntax error?

Hmm. That is a confusing inconsistency, I agree. It is deliberate, and
explicitly documented:

    Note that leading zeros in a non-zero decimal number are not
    allowed. This is for disambiguation with C-style octal literals,
    which Python used before version 3.0.

    <URL:https://docs.python.org/3/reference/lexical_analysis.html#integer-literals>

which does not explain why “non-zero decimal number” was chosen, rather
than simply any decimal number.

> But then why is 00...0 valid, that is, does not give a syntax error?

At one level, the answer is: because the language reference declares
those rules for the syntax.

At another level, the answer is: I don't know why that decision was
made, and on the face of it I disagree.

-- 
 \            “But it is permissible to make a judgment after you have |
  `\    examined the evidence. In some circles it is even encouraged.” |
_o__)                    —Carl Sagan, _The Burden of Skepticism_, 1987 |
Ben Finney