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Why does Python report 0.1 + 0.2 == 0.3 as false?

0.1 has no exact binary form, so it is stored as a close approximation.

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  1. A bug in the processor
  2. The language rounds to 2 places
  3. 0.1 cannot be stored exactly in binary ✔

Why: Computers store floats as binary fractions. Just like 1/3 never ends in decimal, 1/10 never ends in binary. The tiny rounding errors in 0.1 and 0.2 add up, so the sum is 0.30000000000000004.

Huh, didn't know that: Python's docs note this is not a Python bug: the same thing happens in every language that uses your hardware's floating point.

The dad joke
Why did 0.1 and 0.2 break up? They just didn't add up.
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References

Answer: 0.1 cannot be stored exactly in binary. Computers store floats as binary fractions. Just like 1/3 never ends in decimal, 1/10 never ends in binary. The tiny rounding errors in 0.1 and 0.2 add up, so the sum is 0.30000000000000004.

  1. Python docs: Floating-Point Arithmetic, Issues and Limitations docs.python.org/3/tutorial/floatingpoint.html
    no matter how many base 2 digits you're willing to use, the decimal value 0.1 cannot be represented exactly as a base 2 fraction
    Checked 2026-10-10.

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