How to properly round-up half float numbers?

by

The Numeric Types section documents this behaviour explicitly:

round(x[, n])
x rounded to n digits, rounding half to even. If n is omitted, it defaults to 0.

Note the rounding half to even. This is also called bankers rounding; instead of always rounding up or down (compounding rounding errors), by rounding to the nearest even number you average out rounding errors.

If you need more control over the rounding behaviour, use the decimal module, which lets you specify exactly what rounding strategy should be used.

For example, to round up from half:

>>> from decimal import localcontext, Decimal, ROUND_HALF_UP
>>> with localcontext() as ctx:
...     ctx.rounding = ROUND_HALF_UP
...     for i in range(1, 15, 2):
...         n = Decimal(i) / 2
...         print(n, '=>', n.to_integral_value())
...
0.5 => 1
1.5 => 2
2.5 => 3
3.5 => 4
4.5 => 5
5.5 => 6
6.5 => 7

More Related Contents:

  1. Limiting floats to two decimal points
  2. rounding errors in Python floor division
  3. Need a python module for numerical and scientific computing other than NumPy and SciPy
  4. Python 3.x rounding behavior
  5. How do you round UP a number?
  6. How to avoid floating point errors? [duplicate]
  7. round() doesn’t seem to be rounding properly
  8. Pandas read csv file with float values results in weird rounding and decimal digits
  9. Floating Point Limitations [duplicate]
  10. Rounding a number in Python but keeping ending zeros
  11. Convert float to string in positional format (without scientific notation and false precision)
  12. What is the difference between int() and floor() in Python 3?
  13. Clarification on the Decimal type in Python
  14. Determine precision and scale of particular number in Python
  15. Why does the floating-point value of 4*0.1 look nice in Python 3 but 3*0.1 doesn’t?
  16. Rounding error in Python with non-odd number? [duplicate]
  17. How to pad a string with leading zeros in Python 3 [duplicate]
  18. How to get largest possible precision? (Python – Decimal)
  19. Rounding floats so that they sum to precisely 1
  20. Round a floating-point number down to the nearest integer?
  21. Print a float number in normal form, not exponential form / scientific notation [duplicate]
  22. ‘is’ operator behaves unexpectedly with floats
  23. Pinging servers in Python
  24. How to get numbers after decimal point?
  25. Generate a random letter in Python
  26. Python 3.1.1 string to hex
  27. pandas or python equivalent of tidyr complete
  28. How do I run python 2 and 3 in windows 7? [duplicate]
  29. Appending to list in Python dictionary [duplicate]
  30. Why doesn’t the operator module have a function for logical or?

Leave a Comment