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.
> 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.
> fraction: "." intpart
> exponent: ("e" | "E") "_"* ["+" | "-"] digit [decimalrest]
This allows underscores in the exponent (1e-5_0), contradicting the
other bullet point.
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