when i try to check whether float variable contain exact integer value i get the folowing strange behaviour. My code :
x = 1.7 print x, (x == int(x))
x += 0.1 print x, (x == int(x))
x += 0.1 print x, (x == int(x))
x += 0.1 print x, (x == int(x))
print "----------------------"
x = **2.7** print x, (x == int(x))
x += 0.1 print x, (x == int(x))
x += 0.1 print x, (x == int(x))
x += 0.1 print x, (x == int(x))
I get the folowing strange output (last line is the problem):
1.7 False
1.8 False
1.9 False
2.0 True
----------------------
2.7 False
2.8 False
2.9 False
3.0 False
Any idea why 2.0
is true
and 3.0
is false
?
the problem is not with conversion but with addition .
int(3.0) == 3.0
returns True
as expected.
The probelm is that floating points are not infinitely accurate, and you cannot expect 2.7 + 0.1 * 3 to be 3.0
>>> 2.7 + 0.1 + 0.1 + 0.1
3.0000000000000004
>>> 2.7 + 0.1 + 0.1 + 0.1 == 3.0
False
As suggested by @SuperBiasedMan it is worth noting that in OPs approach the problem was somehow hidden due to the use of printing (string conversion) which simplifies data representation to maximize readability
>>> print 2.7 + 0.1 + 0.1 + 0.1
3.0
>>> str(2.7 + 0.1 + 0.1 + 0.1)
'3.0'
>>> repr(2.7 + 0.1 + 0.1 + 0.1)
'3.0000000000000004'
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