Rounding floating point numbers to closest multiple of 0.005 with rounding to 3 decimal digits is producing a weird output

Question

I wrote a small piece of code that rounds a number to the closest multiple of 0.005 but it produces a weird output, that I didn't expect. I am using Python version 3.7.3

Here is the code:

number = 1.639
print(5 * round(number / 5, 3))

Output

1.6400000000000001

Expected output

1.64

Check this replit for detailed output on different values.

Can anyone tell me why this happens?

in this cas, is the output should be *1.640* ? – codrelphi Jan 19 '20 at 17:21 — codrelphi, Jan 19 '20 at 17:21
@codrelphi , That is correct – Radwan Abu-Odeh Jan 19 '20 at 17:22 — Radwan Abu-Odeh, Jan 19 '20 at 17:22

score 1 · Accepted Answer · answered Jan 19 '20 at 17:25

1

print(round(5 * round(1.639 / 5, 3), 3))

Round it again since according to what I see you are multiplying the rounded number by 5 then you expect that the number to be rounded. I guess you should round the output of the first rounding step!

answered Jan 19 '20 at 17:25

ksa

118
8

score 1 · Answer 2 · answered Jan 19 '20 at 17:27

If you want to do the multiplication on the rounding number, here is how you can do:

number = 1.639
temp = round(number / 5, 3)
final = round(5 * temp, 3)

print(final) # 1.64

If you just want to round the final result, here is how you can do it:

number = 1.639
final = round(5 * (number / 5), 3)
print(final) # 1.639

Rounding floating point numbers to closest multiple of 0.005 with rounding to 3 decimal digits is producing a weird output

2 Answers2