Message 332975 - Python tracker

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Author	steven.daprano
Recipients	Bart van den Donk, ezio.melotti, mrabarnett, steven.daprano
Date	2019-01-04.13:01:24
SpamBayes Score	-1.0
Marked as misclassified	Yes
Message-id	<1546606884.3.0.373335113122.issue35658@roundup.psfhosted.org>
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Not a bug. 0.1 is a binary floating point value, please read the FAQs: https://docs.python.org/3/faq/design.html#why-are-floating-point-calculations-so-inaccurate 1/10 = 0.1 in decimal cannot be represented exactly in binary floating point, so when you type 0.1 as a float, the actual value you get is the closest number you can get using 53 bits for the significant digits, 8 bits for the exponent and 1 bit for the sign (plus or minus). That is approximately 0.1000000000000000056 or so. Unfortunately you cannot get any closer to 1/10 in binary floating point numbers, for the same reason you cannot get 1/3 exactly in decimal. See also https://stackoverflow.com/questions/8215437/floating-point-accuracy-in-python https://stackoverflow.com/questions/21895756/why-are-floating-point-numbers-inaccurate https://stackoverflow.com/questions/1089018/why-cant-decimal-numbers-be-represented-exactly-in-binary?noredirect=1&lq=1

Not a bug. 0.1 is a binary floating point value, please read the FAQs:

https://docs.python.org/3/faq/design.html#why-are-floating-point-calculations-so-inaccurate

1/10 = 0.1 in decimal cannot be represented *exactly* in binary floating point, so when you type 0.1 as a float, the actual value you get is the closest number you can get using 53 bits for the significant digits, 8 bits for the exponent and 1 bit for the sign (plus or minus). That is approximately 0.1000000000000000056 or so.

Unfortunately you cannot get any closer to 1/10 in binary floating point numbers, for the same reason you cannot get 1/3 exactly in decimal.

See also 

https://stackoverflow.com/questions/8215437/floating-point-accuracy-in-python

https://stackoverflow.com/questions/21895756/why-are-floating-point-numbers-inaccurate

https://stackoverflow.com/questions/1089018/why-cant-decimal-numbers-be-represented-exactly-in-binary?noredirect=1&lq=1

History
Date	User	Action	Args
2019-01-04 13:01:26	steven.daprano	set	recipients: + steven.daprano, ezio.melotti, mrabarnett, Bart van den Donk
2019-01-04 13:01:24	steven.daprano	set	messageid: <1546606884.3.0.373335113122.issue35658@roundup.psfhosted.org>
2019-01-04 13:01:24	steven.daprano	link	issue35658 messages
2019-01-04 13:01:24	steven.daprano	create