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g format differs from Python #88

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jariji opened this issue Oct 21, 2024 · 1 comment · May be fixed by #91
Open

g format differs from Python #88

jariji opened this issue Oct 21, 2024 · 1 comment · May be fixed by #91

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@jariji
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jariji commented Oct 21, 2024

I think this might be a bug.

# Format.jl
julia> pyfmt(".3g", 12.34)
"12.340"

# Python 
In: format(12.34, ".3g")
Out: '12.3'
@R3G3N3R4T0R
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Yes, the implementation is plain wrong. Currently in fmtcore.jl

Format.jl/src/fmtcore.jl

Lines 337 to 341 in 37c24b9

if 1.0e-4 <= ax < 1.0e6
_pfmt_f(out, fs, x)
else
_pfmt_e(out, fs, x)
end

fs is passed without regard on how to handle significant digits. The correct behavior is documented in Python's Format String documentation this repo referenced to.
I will see if I can do anything, currently this gives the correct behavior but I am not sure this is how they do it.

function _pfmt_g(out::IO, fs::FormatSpec, x::AbstractFloat)
    # number decomposition
    ax = abs(x)
    if 1.0e-4 <= ax < 1.0e6
        newprec = fs.prec - floor(Int, log10(x)) - 1
        _pfmt_f(out, FormatSpec(fs ;prec=newprec), x)
    else
        newprec = fs.prec - 1
        _pfmt_e(out, FormatSpec(fs ;prec=newprec), x)
    end
end

@R3G3N3R4T0R R3G3N3R4T0R linked a pull request Mar 3, 2025 that will close this issue
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Correct format gG precision handling R3G3N3R4T0R/Format.jl
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@R3G3N3R4T0R @jariji