Rounding issue python

Asked Oct 31 '18 at 14:19

Active Oct 31 '18 at 14:25

Viewed 20 times

I have two functions:

def centify(amount_nbr):
    if amount_nbr:
        try:
            amount_nbr = int(float(amount_nbr) * 100)
        except ValueError:
            amount_nbr = 0
    else:
        amount_nbr = 0
    return amount_nbr

def uncentify(amount_nbr):
    if amount_nbr:
        amount_nbr /= 100.
    else:
        amount_nbr = 0
    return amount_nbr

When I test a load of floats:

for i in range(0, 100):
    i *= 0.01
    if i != uncentify(centify(i)):
        print "%f - %f" % (uncentify(centify(i)), i)

It returns that the rounding is wrong for:

0.280000 - 0.290000
0.350000 - 0.350000
0.410000 - 0.410000
0.470000 - 0.470000
0.570000 - 0.570000
0.570000 - 0.580000
0.690000 - 0.690000
0.700000 - 0.700000
0.820000 - 0.820000
0.830000 - 0.830000
0.940000 - 0.940000
0.950000 - 0.950000

What is going on? And how do I make them the exact inverse?

I need to fix the fact that:

num = 316805.79
print centify(num)

returns 31680578 rather than 31680579

edited Oct 31 '18 at 14:25

asked Oct 31 '18 at 14:19

maxisme

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What are you expecting it to print? – OneCricketeer Oct 31 '18 at 14:21
Nothing! as they all should be the same! – maxisme Oct 31 '18 at 14:22
looks like you want to use https://docs.python.org/3/library/decimal.html#module-decimal – hiro protagonist Oct 31 '18 at 14:23
I would suggest you try printing the actual float value, not strings, since that's what you're comparing – OneCricketeer Oct 31 '18 at 14:24

Rounding issue python

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