Python で半浮動小数点数の一貫した丸め動作を確保するにはどうすればよいですか?

Rounding Half Float Numbers: Understanding Rounding Behavior and Alternative Approaches

When rounding half float numbers using the round() function, programmers may encounter unexpected behavior. As demonstrated in the example code, floating values are rounded to the nearest even number instead of being consistently rounded up. This is attributed to the "rounding half to even" behavior documented in the Numeric Types section for round().

To achieve accurate rounding, it is recommended to utilize the decimal module, which provides control over rounding strategies. By specifying the ROUND_HALF_UP rounding strategy within a local context, you can ensure that values are consistently rounded up from half. The following code snippet illustrates this approach:

<code class="python">from decimal import localcontext, Decimal, ROUND_HALF_UP

with localcontext() as ctx:
    ctx.rounding = ROUND_HALF_UP
    for i in range(1, 15, 2):
        n = Decimal(i) / 2
        print(n, '=&gt;', n.to_integral_value())</code>

Output:

0.5 => 1
1.5 => 2
2.5 => 3
3.5 => 4
4.5 => 5
5.5 => 6
6.5 => 7

By employing this approach, you gain precise control over rounding behavior and can avoid unexpected outcomes.

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