CODEWITHSUNDEEP
pythonnumpymath
camilogutierrez
camilogutierrez

Reputation: 66

Why math.trunc do not work as expected in Python?

I try to run the following. I was expecting the integer part (151511919299292911851) but I get a value of 151511919299292921856 that is -10005 less than what I expected.

import math
math.trunc(float('151511919299292911851.06'))

Upvotes: 0

Views: 381

Answers (1)

Peter O.
Peter O.

Reputation: 32878

This is caused by the limited precision (usually 53 significant bits) supported by float values. To avoid this, use the arbitrary-precision Fraction class from Python's fractions module:


In [32]: from fractions import Fraction                                         

In [35]: import math                                                            

In [38]: math.trunc(Fraction('151511919299292911851.06'))                       
Out[38]: 151511919299292911851

In [39]: math.trunc(float('151511919299292911851.06'))                          
Out[39]: 151511919299292921856

In [40]: math.trunc(float('-151511919299292911851.06'))                         
Out[40]: -151511919299292921856

In [41]: math.trunc(Fraction('-151511919299292911851.06'))                      
Out[41]: -151511919299292911851

Upvotes: 3

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