python data_error ai_generated true

AssertionError: assert 0.30000000000000004 == 0.3 E + 其中 0.30000000000000004 = 0.1 + 0.2

AssertionError: assert 0.30000000000000004 == 0.3 E + where 0.30000000000000004 = 0.1 + 0.2

ID: python/pytest-assertion-approx-float

其他格式: JSON · Markdown 中文 · English
80%修复率
90%置信度
0证据数
2025-02-03首次发现

版本兼容性

版本状态引入弃用备注
7.x active — — —
8.x active — — —

根因分析

二进制浮点表示无法精确表示 0.3；直接对浮点数使用相等比较不可靠。

English

Binary floating-point representation cannot represent 0.3 exactly; direct equality on floats is unreliable.

generic

解决方案

  1. 98% 成功率 
    import pytest

def test_sum():
    assert 0.1 + 0.2 == pytest.approx(0.3)
    assert [0.1, 0.2] == pytest.approx([0.1, 0.2])
  2. 95% 成功率 
    import math

def test_sum():
    assert math.isclose(0.1 + 0.2, 0.3, rel_tol=1e-9, abs_tol=1e-12)

无效尝试

常见但无效的做法:

  1. 50% 失败

    Works for some values but fails for very large or very small magnitudes; not a general solution.

  2. 70% 失败

    String representations vary across Python versions and locales; brittle.