Specifying number of decimal places in Python

Question

When accepting user input with a decimal in Python I m using      will input meal subtotal   def input meal          mealPrice   input  Enter the meal subtotal            mealPrice   float  mealPrice        return mealPrice     which returns exactly what is entered - say  43 45 but when using that value to calculate and display tax I m using      will calculate 6  tax   def calc tax mealPrice         tax   mealPrice  06       return tax   which returns a display of   2 607 using      mealPrice   input meal   tax   calc tax mealPrice  display data mealPrice  tax      How can I set that to  2 61 instead  Forgive me  I realize this is basic stuff but they don t call it Intro for nothing     Thanks

User · Answer

You don t show the code for display data  but here s what you need to do   print    0 02f   amount   This is a format specifier for the variable amount   Since this is beginner topic  I won t get into floating point rounding error  but it s good to be aware that it exists

User · Answer

To calculate tax  you could use round  after all  that s what the restaurant does    def calc tax mealPrice         tax   round mealPrice  06 2      return tax   To display the data  you could use a multi-line string  and the string format method    def display data mealPrice  tax       total round mealPrice tax 2      print      Your Meal Price is  m  5 2f  Tax                 x  5 2f  Total               t  5 2f      format m mealPrice x tax t total     Note the format method was introduced in Python 2 6  for earlier versions you ll need to use old-style string interpolation         print      Your Meal Price is  5 2f Tax                 5 2f Total               5 2f      mealPrice tax total     Then   mealPrice input meal   tax calc tax mealPrice  display data mealPrice tax    yields     Enter the meal subtotal   43 45   Your Meal Price is 43 45   Tax                 2 61   Total              46 06

User · Answer

This standard library solution likely has not been mentioned because the question is so dated  While these answers may scale to the other use cases beyond currency where differing levels of decimals are required  it seems you need it for currency   I recommend you use the standard library locale currency object  It seems to have been created to address this problem of currency representation    import locale locale setlocale locale LC ALL   en US UTF-8    locale currency 1 23   gt  gt  gt   1 23  locale currency 1 53251   gt  gt  gt   1 23  locale currency 1   gt  gt  gt   1 00   locale currency mealPrice    Currency generalizes to other countries as well

User · Answer

There s a few ways to do this depending on how you want to hold the value   You can use basic string formatting  e g   Your Meal Price is   2f     mealPrice   You can modify the 2 to whatever precision you need   However  since you re dealing with money you should look into the decimal module which has a cool method named quantize which is exactly for working with monetary applications  You can use it like so   from decimal import Decimal  ROUND DOWN mealPrice   Decimal str mealPrice   quantize Decimal   01    rounding ROUND DOWN    Note that the rounding attribute is purely optional as well

User · Answer

Use round   function  round 2 607    3 round 2 607 2    2 61

User · Answer

I m astonished by the second number you mention  and confirm by your requested rounding  -- at first I thought my instinct for mental arithmetic was starting to fail me  I am getting older  after all  so that might be going the same way as my once-sharp memory -     but then I confirmed it hasn t  yet  by using  as I imagine you are  Python 3 1  and copying and pasting      gt  gt  gt  def input meal              mealPrice   input  Enter the meal subtotal                mealPrice   float  mealPrice            return mealPrice         gt  gt  gt  def calc tax mealPrice             tax   mealPrice  06           return tax       gt  gt  gt  m   input meal   Enter the meal subtotal   34 45  gt  gt  gt  print calc tax m   2 067  gt  gt  gt        as expected -- yet  you say it instead  returns a display of   2 607     which might be a typo  just swapping two digits  except that you then ask  How can I set that to  2 61 instead   so it really seems you truly mean 2 607  which might be rounded to 2 61 in various ways  and definitely not the arithmetically correct result  2 067  which at best might be rounded to 2 07    definitely not to 2 61 as you request      I imagine you first had the typo occur in transcription  and then mentally computed the desired rounding from the falsified-by-typo 2 607 rather than the actual original result -- is that what happened   It sure managed to confuse me for a while -   Anyway  to round a float to two decimal digits  simplest approach is the built-in function round with a second argument of 2    gt  gt  gt  round 2 067  2  2 07  gt  gt  gt  round 2 607  2  2 61   For numbers exactly equidistant between two possibilities  it rounds-to-even    gt  gt  gt  round 2 605  2  2 6  gt  gt  gt  round 2 615  2  2 62   or  as the docs put it  exemplifying with the single-argument form of round  which rounds to the closest integer       if two multiples are equally close  rounding is done toward the   even choice  so  for example  both   round 0 5  and round -0 5  are 0  and   round 1 5  is 2     However  for computations on money  I second the recommendation  already given in other answers  to stick with what the decimal module offers  instead of float numbers

[python] Specifying number of decimal places in Python

Examples related to python