How to round to 2 decimals with Python

Question

I am getting a lot of decimals in the output of this code  Fahrenheit to Celsius converter    My code currently looks like this   def main        printC formeln typeHere      def typeHere        global Fahrenheit     try          Fahrenheit   int raw input  Hi  Enter Fahrenheit value  and get it in Celsius  n        except ValueError          print   nYour insertion was not a digit           print  We ve put your Fahrenheit value to 50           Fahrenheit   50     return Fahrenheit  def formeln c       Celsius    Fahrenheit - 32 00    5 00 9 00     return Celsius  def printC answer       answer   str answer      print   nYour Celsius value is     answer     C  n     main     So my question is  how do I make the program round every answer to the 2nd decimal place

User · Answer

You can use round operator for up to 2 decimal   num   round 343 5544  2  print num     output is 343 55

User · Answer

round 12 3956 - 0 005  2     minus 0 005  then round    The answer is from  https   stackoverflow com a 29651462 8025086

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As you want your answer in decimal number so you dont need to typecast your answer variable to str in printC   function    and then use printf-style String Formatting

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If you need avoid floating point problem on rounding numbers for accounting  you can use numpy round   You need install numpy     pip install numpy   and the code     import numpy as np  print round 2 675  2   print float np round 2 675  2      prints  2 67 2 68   You should use that if you manage money with legal rounding

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You can use the string formatting operator of python         2f  means 2 digits after the decimal point   def typeHere        try          Fahrenheit   int raw input  Hi  Enter Fahrenheit value  and get it in Celsius  n        except ValueError          print   nYour insertion was not a digit           print  We ve put your Fahrenheit value to 50           Fahrenheit   50     return Fahrenheit  def formeln Fahrenheit       Celsius    Fahrenheit - 32 0    5 0 9 0     return Celsius  def printC answer       print   nYour Celsius value is   2f C  n    answer  def main        printC formeln typeHere      main     http   docs python org 2 library stdtypes html string-formatting

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If you need not only round result but elso do math operations with round result  then you can use decimal Decimal https   docs python org 2 library decimal html from decimal import Decimal  ROUND DOWN  Decimal  7 325   quantize Decimal   01    rounding ROUND DOWN  Decimal  7 32

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You can use the round function  round 80 23456  3   will give you an answer of 80 234 In your case  use answer   str round answer  2

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Most answers suggested round or format  round sometimes rounds up  and in my case I needed the value of my variable to be rounded down and not just displayed as such   round 2 357  2     - gt  2 36   I found the answer here  How do I round a floating point number up to a certain decimal place   import math v   2 357 print math ceil v 100  100     - gt  2 36 print math floor v 100  100     - gt  2 35   or   from math import floor  ceil  def roundDown n  d 8       d   int  1      0    d       return floor n   d    d  def roundUp n  d 8       d   int  1      0    d       return ceil n   d    d

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Here is an example that I used   def volume self       return round pi   self radius    2   self height  2   def surface area self       return round  2   pi   self radius   self height     2   pi   self radius    2   2

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float str round answer  2    float str round 0 0556781255  2

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You want to round your answer   round value significantDigit  is the ordinary solution to do this  however this sometimes does not operate as one would expect from a math perspective when the digit immediately inferior  to the left of  the digit you re rounding to has a 5   Here s some examples of this unpredictable behavior    gt  gt  gt  round 1 0005 3  1 0  gt  gt  gt  round 2 0005 3  2 001  gt  gt  gt  round 3 0005 3  3 001  gt  gt  gt  round 4 0005 3  4 0  gt  gt  gt  round 1 005 2  1 0  gt  gt  gt  round 5 005 2  5 0  gt  gt  gt  round 6 005 2  6 0  gt  gt  gt  round 7 005 2  7 0  gt  gt  gt  round 3 005 2  3 0  gt  gt  gt  round 8 005 2  8 01   Assuming your intent is to do the traditional rounding for statistics in the sciences  this is a handy wrapper to get the round function working as expected needing to import extra stuff like Decimal    gt  gt  gt  round 0 075 2   0 07   gt  gt  gt  round 0 075 10   -2 6  2   0 08   Aha  So based on this we can make a function     def roundTraditional val digits      return round val 10   -len str val  -1   digits    Basically this adds a really small value to the string to force it to round up properly on the unpredictable instances where it doesn t ordinarily with the round function when you expect it to   A convenient value to add is 1e-X where X is the length of the number string you re trying to use round on plus 1    The approach of using 10   -len val -1  was deliberate  as it the largest small number you can add to force the shift  while also ensuring that the value you add never changes the rounding even if the decimal   is missing   I could use just 10   -len val   with a condiditional if  val gt 1  to subtract 1 more    but it s simpler to just always subtract the 1 as that won t change much the applicable range of decimal numbers this workaround can properly handle   This approach will fail if your values reaches the limits of the type  this will fail  but for nearly the entire range of valid decimal values it should work   So the finished code will be something like   def main        printC formeln typeHere      def roundTraditional val digits       return round val 10   -len str val  -1    def typeHere        global Fahrenheit     try          Fahrenheit   int raw input  Hi  Enter Fahrenheit value  and get it in Celsius  n        except ValueError          print   nYour insertion was not a digit           print  We ve put your Fahrenheit value to 50           Fahrenheit   50     return Fahrenheit  def formeln c       Celsius    Fahrenheit - 32 00    5 00 9 00     return Celsius  def printC answer       answer   str roundTraditional answer 2       print   nYour Celsius value is     answer     C  n   main        should give you the results you expect   You can also use the decimal library to accomplish this  but the wrapper I propose is simpler and may be preferred in some cases     Edit  Thanks Blckknght for pointing out that the 5 fringe case occurs only for certain values here

User · Answer

Using str format   s syntax to display answer with two decimal places  without altering the underlying value of answer    def printC answer       print   nYour Celsius value is   0 2f   C  n  format answer     Where      introduces the format spec 0 enables sign-aware zero-padding for numeric types  2 sets the precision to 2 f displays the number as a fixed-point number

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You can use the round function  which takes as its first argument the number and the second argument is the precision after the decimal point   In your case  it would be   answer   str round answer  2

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Not sure why  but    0 2f   format 0 5357706  gives me  0 54   The only solution that works for me  python 3 6  is the following   def ceil floor x       import math     return math ceil x  if x  lt  0 else math floor x   def round n digits x  n       import math     return ceil floor x   math pow 10  n     math pow 10  n   round n digits -0 5357706  2  - gt  -0 53  round n digits 0 5357706  2  - gt  0 53

User · Answer

Just use the formatting with   2f which gives you rounding down to 2 decimals   def printC answer       print   nYour Celsius value is   2f C  n    answer

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If you just want to print the rounded result out  you can use the f-strings introduced since Python 3 6  The syntax is the same as str format   s format string syntax  except you put a f in front of the literal string  and you put the variables directly in the string  within the curly braces   2f indicates rounding to two decimal places  number   3 1415926 print f quot The number rounded to two decimal places is  number  2f  quot    Output  The number rounded to two decimal places is 3 14

[python] How to round to 2 decimals with Python?

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