Why .05+.01 == .06 return False in python 2.7.3?

Question

As per my expectation .05+.01 should be equal to .06 but in python its not happening. As .05+.01 = 0.060000000000000005 and that is not equal to .06.

>>> .01+.01
0.02
>>> .02+.01
0.03
>>> .03+.01
0.04
>>> .04+.01
0.05
>>> .05+.01
0.060000000000000005  #expected .06
>>> .06+.01
0.06999999999999999  #expected .07
>>> .07+.01
0.08
>>> .08+.01
0.09
>>> .09+.01
0.09999999999999999 #expected .10
>>> 0.09999999999999999+.01
0.10999999999999999  #expected .11

what is the reason for this?

Obligatory: http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html — NWard, Dec 23 '13 at 10:35
This was already asked: http://stackoverflow.com/questions/11950819/python-math-is-wrong — Bunyk, Dec 23 '13 at 10:38

score 9 · Answer 1 · answered Dec 23 '13 at 10:34

9

Because Python uses IEEE-754 floating point numbers, which are not perfectly precise. The iconic example is 0.1 + 0.2 = 0.30000000000000004.

This is well documented in the Python docs.

answered Dec 23 '13 at 10:34

T.J. Crowder

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score 4 · Answer 2 · answered Dec 23 '13 at 10:34

4

The values you're working with are floating point numbers, see also: http://docs.python.org/2/tutorial/floatingpoint.html

answered Dec 23 '13 at 10:34

Bart Enkelaar

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score 4 · Answer 3 · edited Dec 23 '13 at 10:38

4

Because 0.01 and 0.05 are not what they are looking:

>>> import decimal
>>> decimal.Decimal(0.01)
Decimal('0.01000000000000000020816681711721685132943093776702880859375')
>>> decimal.Decimal(0.05)
Decimal('0.05000000000000000277555756156289135105907917022705078125')

edited Dec 23 '13 at 10:38

wimh

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answered Dec 23 '13 at 10:36

alko

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Why .05+.01 == .06 return False in python 2.7.3?

3 Answers3