Asserting two floats are equal

Question

The following code gives an AssertionError in the last line. However both values are printed as 10.0833333333.

p = [0,1,2,3,4,6,2,2,4,1,2,4]
cell11 = p[0:3]
cell12 = p[3:6]
cell21 = p[6:9]
cell22 = p[9:12]

x11 = sum(cell11)/float(3)
x12 = sum(cell12)/float(3)
x21 = sum(cell21)/float(3)
x22 = sum(cell22)/float(3)
x1dot = (x11+x12)/float(2)
x2dot = (x21+x22)/float(2)
xdot1 = (x11+x21)/float(2)
xdot2 = (x12+x22)/float(2)
xdotdot = (x1dot+x2dot)/float(2)
assert(xdotdot == (xdot1+xdot2)/float(2))
n=3
x11diff = ((x11-xdotdot) - (x1dot-xdotdot) - (xdot1-xdotdot))**2
x12diff = ((x12-xdotdot) - (x1dot-xdotdot) - (xdot2-xdotdot))**2
x21diff = ((x21-xdotdot) - (x2dot-xdotdot) - (xdot1-xdotdot))**2
x22diff = ((x22-xdotdot) - (x2dot-xdotdot) - (xdot2-xdotdot))**2
ssaxb = n*(x11diff+x12diff+x21diff+x22diff)
print str(ssaxb)
print str(10+(1/float(12)))
assert(ssaxb == 10+(1/float(12)))

Are ssaxb and 10+(1/float(12)) somehow stored as slightly different values?

don't convert to `str()` prior to printing and you will see the `float`s are different — Chris_Rands, Feb 26 '19 at 21:44
https://docs.scipy.org/doc/numpy-1.15.0/reference/generated/numpy.isclose.html — mad_, Feb 26 '19 at 21:46
@Chris_Rands But OP is not checking str values. It is just used while printing — mad_, Feb 26 '19 at 21:49
@Chris_Rands actually they look the same even without the `str()` — Bjørn Kjos-Hanssen, Feb 26 '19 at 21:50
@mad_ exactly, read what i wrote again. `print(ssaxb, 10+(1/float(12)))` > `10.083333333333329 10.083333333333334` — Chris_Rands, Feb 26 '19 at 21:54

score 0 · Answer 1 · answered Feb 26 '19 at 22:01

0

As pointed out by @Chris_Rands printing the values will give you the reason why assert statement is failing as float values are different

import numpy as np

print(ssaxb, 10+(1/float(12)))  #(10.08333333333333, 10.083333333333334)

assert(np.isclose(ssaxb, 10+(1/float(12))))

assert(round(ssaxb,7),round(10+(1/float(12)),7))

answered Feb 26 '19 at 22:01

mad_

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Reason for downvoting, please? – mad_ Feb 26 '19 at 22:12
1

1. numpy is not otherwise mentioned so should use `math.isclose` 2. don't answer obvious dupes, just close vote. – wim Feb 26 '19 at 22:14

Asserting two floats are equal

1 Answers1