How to round a floating point number up to a certain decimal place

Question

Suppose I have 8 8333333333333339  and I want to convert it to 8 84  How can I accomplish this in Python   round 8 8333333333333339  2  gives 8 83 and not 8 84  I am new to Python or programming in general   I don t want to print it as a string  and the result will be further used  For more information on the problem  please check Tim Wilson s Python Programming Tips  Loan and payment calculator

User · Accepted Answer

8 833333333339  or 8 833333333333334  the result of 106 00 12  properly rounded to two decimal places is 8 83  Mathematically it sounds like what you want is a ceiling function  The one in Python s math module is named ceil  import math  v   8 8333333333333339 print math ceil v 100  100     - gt  8 84  Respectively  the floor and ceiling functions generally map a real number to the largest previous or smallest following integer which has zero decimal places     so to use them for 2 decimal places the number is first multiplied by 102  or 100  to shift the decimal point and is then divided by it afterwards to compensate  If you don t want to use the math module for some reason  you can use this  minimally tested  implementation I just wrote  def ceiling x       n   int x      return n if n-1  lt  x  lt   n else n 1  How all this relates to the linked Loan and payment calculator problem   From the sample output it appears that they rounded up the monthly payment  which is what many call the effect of the ceiling function  This means that each month a little more than 1 12 of the total amount is being paid  That made the final payment a little smaller than usual     leaving a remaining unpaid balance of only 8 76  It would have been equally valid to use normal rounding producing a monthly payment of 8 83 and a slightly higher final payment of 8 87  However  in the real world people generally don t like to have their payments go up  so rounding up each payment is the common practice     it also returns the money to the lender more quickly

User · Answer

Here is my solution for the round up down problem   lt   5  round down   gt     5  round up     import math  def  should round down val  float       if val  lt  0          return   val   -1    1   lt  0 5     return  val   1   lt  0 5  def  round val  float  ndigits 0       if ndigits  gt  0          val    10     ndigits - 1      is positive   val  gt  0     tmp val   val     if not is positive          tmp val    -1     rounded value   math floor tmp val  if  should round down val  else math ceil tmp val      if not is positive          rounded value    -1     if ndigits  gt  0          rounded value    10     ndigits - 1      return rounded value    test   nr   12 2548   for digit in range 0  4         print     decimals      - gt      format digit  nr   round nr  digit       output   0 decimals   12 2548 - gt  12   1 decimals   12 2548 - gt  12 0   2 decimals   12 2548 - gt  12 3   3 decimals   12 2548 - gt  12 25

User · Answer

The easiest way to do this is by using the below function  which is built in   format     For example   format 1 242563   2f     The output would be   1 24   Similarly   format 9 165654   1f     would give   9 2

User · Answer

A much simpler way is to simply use the round   function  Here is an example   total price   float   price 1   2 99 price 2   0 99 total price   price 1   price 2   If you were to print out total price right now you would get  3 9800000000000004   But if you enclose it in a round   function like so  print round total price 2     The output equals  3 98   The round   function works by accepting two parameters  The first is the number you want to round  The second is the number of decimal places to round to

User · Answer

You want to use the decimal module but you also need to specify the rounding mode  Here s an example    gt  gt  gt  import decimal  gt  gt  gt  decimal Decimal  8 333333   quantize decimal Decimal   01    rounding decimal ROUND UP  Decimal  8 34    gt  gt  gt  decimal Decimal  8 333333   quantize decimal Decimal   01    rounding decimal ROUND DOWN  Decimal  8 33    gt  gt  gt

User · Answer

Use the decimal module  http   docs python org library decimal html

User · Answer

If you round 8 8333333333339 to 2 decimals  the correct answer is 8 83  not 8 84  The reason you got 8 83000000001 is because 8 83 is a number that cannot be correctly reprecented in binary  and it gives you the closest one  If you want to print it without all the zeros  do as VGE says   print    2f    8 833333333339     Replace number with the variable

User · Answer

This is normal  and has nothing to do with Python  because 8 83 cannot be represented exactly as a binary float  just as 1 3 cannot be represented exactly in decimal  0 333333    ad infinitum    If you want to ensure absolute precision  you need the decimal module    gt  gt  gt  import decimal  gt  gt  gt  a   decimal Decimal  8 833333333339    gt  gt  gt  print round a 2   8 83

User · Answer

I have this code   tax    tax   100    price   and then this code   tax   round  tax   100    price  2    round worked for me

User · Answer

Here is a simple function to do this for you   def precision num x       return   0  xf   format round num     Here  num is the decimal number  x is the decimal up to where you want to round a floating number   The advantage over other implementation is that it can fill zeros at the right end of the decimal to make a deciaml number up to x decimal places   Example 1   precision 10 2  9    will return   10 200000000  up to 9 decimal points   Example 2   precision 10 2231  2    will return  10 22  up to two decimal points

User · Answer

If you want to round  8 84 is the incorrect answer  8 833333333333 rounded is 8 83 not 8 84  If you want to always round up  then you can use math ceil  Do both in a combination with string formatting  because rounding a float number itself doesn t make sense      2f     math ceil x   100    100

User · Answer

Just for the record   You could do it this way   def roundno no       return int no  1     no 1  0 5   1    There  no need for includes imports

[python] How to round a floating point number up to a certain decimal place?

How all this relates to the linked Loan and payment calculator problem:

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