Handling long integer-divisions in python [duplicate]

Question

I observed data loss in python integer division. Below is a sample:

In [37]: 1881676377427221798261593926550420634004875213170503083 * 123456789789456123
Out[37]: 232305724979817822068561403710502859128427941904411569030164388864727209

In [38]: int(232305724979817822068561403710502859128427941904411569030164388864727209 / 123456789789456123)
Out[38]: 1881676377427221679799422390196630516487239698149801984

In [39]: 232305724979817822068561403710502859128427941904411569030164388864727209 / 123456789789456123
Out[39]: 1.8816763774272217e+54

Observation: Over multiple attempts with random long integers, I observed that the numbers seem to differ near about where it loses precision in the mantissa-exponent format.

Can anyone please help me know where I am missing? (Or is this really a limitation!)

Use // rather than /? For any integers a,b (even with hundreds of digits) a*b//b will always equal a. If you have a situation where integer division isn't adequate, use the fractions or decimal module. — John Coleman
– John Coleman, Commented Feb 11, 2019 at 20:34
/ does a float division, and you run into floating point limitations. use // — Paritosh Singh
– Paritosh Singh, Commented Feb 11, 2019 at 20:34
You are using true division. This always resultsin a float object, which has a fixed sized. If you have int objects, and want no loss of precision, use the integer division operator: // int objects in Python are arbitrarily sized. As long as you have the memory/address space, you can do it. — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Feb 11, 2019 at 20:34

Xorgon · Accepted Answer · 2019-02-11 20:34:30Z

3

In Python 3 integer division is no longer the default. If you would like to use integer division in Python 3 you need to use the // operator rather than /.

>>> 232305724979817822068561403710502859128427941904411569030164388864727209 / 123456789789456123
1.8816763774272217e+54

>>> 232305724979817822068561403710502859128427941904411569030164388864727209 // 123456789789456123
1881676377427221798261593926550420634004875213170503083

answered Feb 11, 2019 at 20:34

Xorgon

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