On 02/11/2016 02:16 AM, Martin Panter wrote:
> I have occasionally wondered about this missing feature.
>
> On 10 February 2016 at 22:20, Georg Brandl <g.bra...@gmx.net> wrote:
>> Abstract and Rationale
>> ======================
>>
>> This PEP proposes to extend Python's syntax so that underscores can be used
>> in
>> integral and floating-point number literals.
>
> This should extend complex or imaginary literals like 10_000j for consistency.
Yes, that was always the case, but I guess it should be explicit.
>> Specification
>> =============
>>
>> * Trailing underscores are not allowed, because they look confusing and don't
>> contribute much to readability.
>> * No underscore allowed after a sign in an exponent (``1e-_5``), because
>> underscores can also not be used after the signs in front of the number
>> (``-1e5``).
>> [. . .]
>>
>> The production list for integer literals would therefore look like this::
>>
>> integer: decimalinteger | octinteger | hexinteger | bininteger
>> decimalinteger: nonzerodigit [decimalrest] | "0" [("0" | "_")* "0"]
>> nonzerodigit: "1"..."9"
>> decimalrest: (digit | "_")* digit
>> digit: "0"..."9"
>> octinteger: "0" ("o" | "O") (octdigit | "_")* octdigit
>> hexinteger: "0" ("x" | "X") (hexdigit | "_")* hexdigit
>> bininteger: "0" ("b" | "B") (bindigit | "_")* bindigit
>> octdigit: "0"..."7"
>> hexdigit: digit | "a"..."f" | "A"..."F"
>> bindigit: "0" | "1"
>>
>> For floating-point literals::
>>
>> floatnumber: pointfloat | exponentfloat
>> pointfloat: [intpart] fraction | intpart "."
>> exponentfloat: (intpart | pointfloat) exponent
>> intpart: digit (digit | "_")*
>
> This allows trailing underscores such as 1_.2, 1.2_, 1.2_e-5. Your
> bullet point above suggests at least some of these are not desired.
The middle one isn't, indeed. I updated the grammar accordingly.
>> fraction: "." intpart
>> exponent: ("e" | "E") "_"* ["+" | "-"] digit [decimalrest]
>
> This allows underscores in the exponent (1e-5_0), contradicting the
> other bullet point.
I clarified the bullet points. An "immediately" was missing.
Thanks for the feedback!
Georg
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