On Mon, Sep 11, 2017 at 06:26:16PM -0600, Neil Schemenauer wrote:
On 2017-09-12, Victor Stinner wrote:
Instead of modifying the Python grammar, the alternative is to enhance float(str) to support it:
k = float("0x1.2492492492492p-3") # 1/7
Making it a different function from float() would avoid backwards compatibility issues. I.e. float() no longer returns errors on some inputs.
I don't think many people will care about backwards compatibility of errors. Intentionally calling float() in order to get an exception is not very common (apart from test suites). Its easier to use raise if you want a ValueError.
The only counter-example I can think of is beginner programmers who write something like:
num = float(input("Enter a number:"))
and are surprised when the "invalid" response "0x1.Fp2" is accepted. But then they've already got the same so-called problem with int accepting "invalid" strings like "0xDEADBEEF". So I stress that this is a problem in theory, not in practice.
from math import hexfloat k = hexfloat("0x1.2492492492492p-3")
I don't think that's necessary. float() is sufficient.
I still think a literal syntax has merits. The above cannot be optimized by the compiler as it doesn't know what hexfloat() refers to. That in turn destroys constant folding peephole stuff that uses the literal.
Indeed. If there are use-cases for hexadecimal floats, then we should support both a literal 0x1.fp2 form and the float constructor.