Array and floating point

[Jonathan Shan]

Hello,

I'm experiencing a problem where the float being appended to the array
is not the same as the result of the appending.

>>from array import *
x = array('f')
x.append(float("0.1"))
x[0]

0.10000000149011612

>>float("0.1")

0.10000000000000001

I'm expecting x[0] = 0.10000000000000001

Thanks
Jonathan Shan

[Peter Otten]

Jonathan Shan wrote:

Hello,

I'm experiencing a problem where the float being appended to the array
is not the same as the result of the appending.

>>>from array import *
x = array('f')
x.append(float("0.1"))
x[0]

0.10000000149011612

>>>float("0.1")

0.10000000000000001

I'm expecting x[0] = 0.10000000000000001

array("f") is an array of C floats while Python's float type is a double in
C terms. That's why you lose some precision. Try array("d") instead:

>>from array import array
x = array("d")
x.append(0.1)
x[0]

0.10000000000000001
Peter

[Robert Kern]

Jonathan Shan wrote:

Hello,

I'm experiencing a problem where the float being appended to the array
is not the same as the result of the appending.

>>>from array import *
x = array('f')
x.append(float("0.1"))
x[0]

0.10000000149011612

>>>float("0.1")

0.10000000000000001

I'm expecting x[0] = 0.10000000000000001

'f' denotes a single-precision floating point number. Python's float objects are
double-precision floating point numbers. Use 'd' instead.

--
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco