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Surprisingly, that is not how rounding works in Python. Rounding half numbers does not round up, and in fact, it doesn't always round down either. Instead, it rounds to the nearest even number. It is worth pointing out that besides the half-number case, round() works as expected, in that it returns the nearest integer.
The Excel ROUNDUP function returns a number rounded up to a given number of decimal places. Unlike standard rounding, where only numbers less than 5 are rounded down, ROUNDUP rounds all numbers up.
The ROUND function rounds a number to a specified number of digits. For example, if cell A1 contains 23.7825, and you want to round that value to two decimal places, you can use the following formula: =ROUND(A1, 2) The result of this function is 23.78.
Put simply, if the last digit is less than 5, round the previous digit down. However, if it's 5 or more than you should round the previous digit up. So, if the number you are about to round is followed by 5, 6, 7, 8, 9 round the number up. And if it is followed by 0, 1, 2, 3, 4 round the number down.
I can't help the way it's stored, but at least formatting works correctly:
'%.1f' % round(n, 1) # Gives you '5.6'
Formatting works correctly even without having to round:
"%.1f" % n
If you use the Decimal module you can approximate without the use of the 'round' function. Here is what I've been using for rounding especially when writing monetary applications:
from decimal import Decimal, ROUND_UP
Decimal(str(16.2)).quantize(Decimal('.01'), rounding=ROUND_UP)
This will return a Decimal Number which is 16.20.
round(5.59, 1) is working fine. The problem is that 5.6 cannot be represented exactly in binary floating point.
>>> 5.6
5.5999999999999996
>>>
As Vinko says, you can use string formatting to do rounding for display.
Python has a module for decimal arithmetic if you need that.
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