Limiting floats to two decimal points

Question

I want a to be rounded to 13 95    gt  gt  gt  a 13 949999999999999  gt  gt  gt  round a  2  13 949999999999999   The round function does not work the way I expected

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lambda x n int x 10n  5  10n has worked for me for many years in many languages

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As  Matt pointed out  Python 3 6 provides f-strings  and they can also use nested parameters   value   2 34558 precision   2 width   4  print f result   value  width   precision f      which will display result  2 35

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lambda x n int x 10n  5  10n has worked for me for many years in many languages

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You are running into the old problem with floating point numbers that not all numbers can be represented exactly  The command line is just showing you the full floating point form from memory   With floating point representation  your rounded version is the same number  Since computers are binary  they store floating point numbers as an integer and then divide it by a power of two so 13 95 will be represented in a similar fashion to 125650429603636838  2  53    Double precision numbers have 53 bits  16 digits  of precision and regular floats have 24 bits  8 digits  of precision  The floating point type in Python uses double precision to store the values   For example    gt  gt  gt  125650429603636838  2  53  13 949999999999999   gt  gt  gt  234042163  2  24  13 949999988079071   gt  gt  gt  a   13 946  gt  gt  gt  print a  13 946  gt  gt  gt  print    2f    a  13 95  gt  gt  gt  round a 2  13 949999999999999  gt  gt  gt  print    2f    round a  2   13 95  gt  gt  gt  print     2f   format a   13 95  gt  gt  gt  print     2f   format round a  2    13 95  gt  gt  gt  print     15f   format round a  2    13 949999999999999   If you are after only two decimal places  to display a currency value  for example   then you have a couple of better choices    Use integers and store values in cents  not dollars and then divide by 100 to convert to dollars  Or use a fixed point number like decimal

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float number   12 234325335563 round float number  2   This will return  12 23  round function takes two arguments  Number to be rounded and the number of decimal places to be returned Here i returned 2 decimal places

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The built-in round   works just fine in Python 2 7 or later   Example    gt  gt  gt  round 14 22222223  2  14 22   Check out the documentation

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For fixing the floating point in type-dynamic languages such as Python and JavaScript  I use this technique    For example  a   70000 b   0 14 c   a   b  print c   Prints 980 0000000002   Try to fix c   int c   10000  100000 print c   Prints 980   You can also use Decimal as following   from decimal import   getcontext   prec   6 Decimal 1    Decimal 7    Results in 6 precision - gt  Decimal  0 142857    getcontext   prec   28 Decimal 1    Decimal 7    Results in 28 precision - gt  Decimal  0 1428571428571428571428571429

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To round a number to a resolution  the best way is the following one  which can work with any resolution  0 01 for two decimals or even other steps     gt  gt  gt  import numpy as np  gt  gt  gt  value   13 949999999999999  gt  gt  gt  resolution   0 01  gt  gt  gt  newValue   int np round value resolution   resolution  gt  gt  gt  print newValue 13 95   gt  gt  gt  resolution   0 5  gt  gt  gt  newValue   int np round value resolution   resolution  gt  gt  gt  print newValue 14 0

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To round a number to a resolution  the best way is the following one  which can work with any resolution  0 01 for two decimals or even other steps     gt  gt  gt  import numpy as np  gt  gt  gt  value   13 949999999999999  gt  gt  gt  resolution   0 01  gt  gt  gt  newValue   int np round value resolution   resolution  gt  gt  gt  print newValue 13 95   gt  gt  gt  resolution   0 5  gt  gt  gt  newValue   int np round value resolution   resolution  gt  gt  gt  print newValue 14 0

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The Python tutorial has an appendix called Floating Point Arithmetic  Issues and Limitations  Read it  It explains what is happening and why Python is doing its best  It has even an example that matches yours  Let me quote a bit     gt  gt  gt  0 1 0 10000000000000001       you may be tempted to use the round     function to chop it back to the single   digit you expect  But that makes no   difference    gt  gt  gt  round 0 1  1  0 10000000000000001       The problem is that the binary   floating-point value stored for    0 1      was already the best possible binary   approximation to 1 10  so trying to   round it again can   t make it better    it was already as good as it gets       Another consequence is that since 0 1   is not exactly 1 10  summing ten   values of 0 1 may not yield exactly   1 0  either    gt  gt  gt  sum   0 0  gt  gt  gt  for i in range 10           sum    0 1      gt  gt  gt  sum 0 99999999999999989    One alternative and solution to your problems would be using the decimal module

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There are new format specifications  String Format Specification Mini-Language   You can do the same as       2f   format 13 949999999999999    Note 1  the above returns a string  In order to get as float  simply wrap with float        float     2f   format 13 949999999999999     Note 2  wrapping with float   doesn t change anything    gt  gt  gt  x   13 949999999999999999  gt  gt  gt  x 13 95  gt  gt  gt  g   float     2f   format x    gt  gt  gt  g 13 95  gt  gt  gt  x    g True  gt  gt  gt  h   round x  2   gt  gt  gt  h 13 95  gt  gt  gt  x    h True

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It s simple like 1 2 3    use decimal module for fast correctly-rounded decimal floating point arithmetic   d Decimal 10000000 0000009    to achieve rounding      d quantize Decimal  0 01      will results with Decimal  10000000 00     make above DRY        def round decimal number  exponent  0 01            decimal value   Decimal number          return decimal value quantize Decimal exponent     OR      def round decimal number  decimal places 2           decimal value   Decimal number          return decimal value quantize Decimal 10     -decimal places     upvote this answer      PS  critique of others  formatting is not rounding

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orig float   232569   16000 0      14 5355625   short float   float     2f   format orig float         14 54

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The Python tutorial has an appendix called Floating Point Arithmetic  Issues and Limitations  Read it  It explains what is happening and why Python is doing its best  It has even an example that matches yours  Let me quote a bit     gt  gt  gt  0 1 0 10000000000000001       you may be tempted to use the round     function to chop it back to the single   digit you expect  But that makes no   difference    gt  gt  gt  round 0 1  1  0 10000000000000001       The problem is that the binary   floating-point value stored for    0 1      was already the best possible binary   approximation to 1 10  so trying to   round it again can   t make it better    it was already as good as it gets       Another consequence is that since 0 1   is not exactly 1 10  summing ten   values of 0 1 may not yield exactly   1 0  either    gt  gt  gt  sum   0 0  gt  gt  gt  for i in range 10           sum    0 1      gt  gt  gt  sum 0 99999999999999989    One alternative and solution to your problems would be using the decimal module

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It s simple like 1 2 3    use decimal module for fast correctly-rounded decimal floating point arithmetic   d Decimal 10000000 0000009    to achieve rounding      d quantize Decimal  0 01      will results with Decimal  10000000 00     make above DRY        def round decimal number  exponent  0 01            decimal value   Decimal number          return decimal value quantize Decimal exponent     OR      def round decimal number  decimal places 2           decimal value   Decimal number          return decimal value quantize Decimal 10     -decimal places     upvote this answer      PS  critique of others  formatting is not rounding

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Most numbers cannot be exactly represented in floats  If you want to round the number because that s what your mathematical formula or algorithm requires  then you want to use round  If you just want to restrict the display to a certain precision  then don t even use round and just format it as that string   If you want to display it with some alternate rounding method  and there are tons  then you need to mix the two approaches     gt  gt  gt     2f    3 14159  3 14   gt  gt  gt     2f    13 9499999  13 95    And lastly  though perhaps most importantly  if you want exact math then you don t want floats at all  The usual example is dealing with money and to store  cents  as an integer

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You are running into the old problem with floating point numbers that not all numbers can be represented exactly  The command line is just showing you the full floating point form from memory   With floating point representation  your rounded version is the same number  Since computers are binary  they store floating point numbers as an integer and then divide it by a power of two so 13 95 will be represented in a similar fashion to 125650429603636838  2  53    Double precision numbers have 53 bits  16 digits  of precision and regular floats have 24 bits  8 digits  of precision  The floating point type in Python uses double precision to store the values   For example    gt  gt  gt  125650429603636838  2  53  13 949999999999999   gt  gt  gt  234042163  2  24  13 949999988079071   gt  gt  gt  a   13 946  gt  gt  gt  print a  13 946  gt  gt  gt  print    2f    a  13 95  gt  gt  gt  round a 2  13 949999999999999  gt  gt  gt  print    2f    round a  2   13 95  gt  gt  gt  print     2f   format a   13 95  gt  gt  gt  print     2f   format round a  2    13 95  gt  gt  gt  print     15f   format round a  2    13 949999999999999   If you are after only two decimal places  to display a currency value  for example   then you have a couple of better choices    Use integers and store values in cents  not dollars and then divide by 100 to convert to dollars  Or use a fixed point number like decimal

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It s doing exactly what you told it to do and is working correctly  Read more about floating point confusion and maybe try decimal objects instead

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from decimal import Decimal   def round float v  ndigits 2  rt str False       d   Decimal v      v str      0   sf     ndigits  format round d  ndigits       if rt str          return v str     return Decimal v str    Results   Python 3 6 1  default  Dec 11 2018  17 41 10   gt  gt  gt  round float 3 1415926  Decimal  3 14    gt  gt  gt  round float 3 1445926  Decimal  3 14    gt  gt  gt  round float 3 1455926  Decimal  3 15    gt  gt  gt  round float 3 1455926  rt str True   3 15   gt  gt  gt  str round float 3 1455926    3 15

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The answers I saw didn t work with the float 52 15  case  After some tests  there is the solution that I m using  import decimal          def value to decimal value  decimal places       decimal getcontext   rounding   decimal ROUND HALF UP    define rounding method     return decimal Decimal str float value    quantize decimal Decimal  1e-    format decimal places      The conversion of the  value  to float and then string is very important  that way   value  can be of the type float  decimal  integer or string   Hope this helps anyone

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from decimal import Decimal   def round float v  ndigits 2  rt str False       d   Decimal v      v str      0   sf     ndigits  format round d  ndigits       if rt str          return v str     return Decimal v str    Results   Python 3 6 1  default  Dec 11 2018  17 41 10   gt  gt  gt  round float 3 1415926  Decimal  3 14    gt  gt  gt  round float 3 1445926  Decimal  3 14    gt  gt  gt  round float 3 1455926  Decimal  3 15    gt  gt  gt  round float 3 1455926  rt str True   3 15   gt  gt  gt  str round float 3 1455926    3 15

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There are new format specifications  String Format Specification Mini-Language   You can do the same as       2f   format 13 949999999999999    Note 1  the above returns a string  In order to get as float  simply wrap with float        float     2f   format 13 949999999999999     Note 2  wrapping with float   doesn t change anything    gt  gt  gt  x   13 949999999999999999  gt  gt  gt  x 13 95  gt  gt  gt  g   float     2f   format x    gt  gt  gt  g 13 95  gt  gt  gt  x    g True  gt  gt  gt  h   round x  2   gt  gt  gt  h 13 95  gt  gt  gt  x    h True

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It s doing exactly what you told it to do and is working correctly  Read more about floating point confusion and maybe try decimal objects instead

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What about a lambda function like this   arred   lambda x n   x  10  n   1  10  n    This way you could just do    arred 3 141591657 2    and get   3 14

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TLDR    The rounding problem of input   output has been solved definitively by Python 2 7 0 and 3 1  A correctly rounded number can be reversibly converted back and forth  str - gt  float   - gt  repr   - gt  float       or Decimal - gt  float - gt  str - gt  Decimal A Decimal type is not necessary for storage anymore    Naturally  it can be necessary to round a result of addition or subtraction of rounded numbers to eliminate the accumulated last bit errors  An explicit Decimal arithmetic can be still handy  but a conversion to string by str    that is with rounding to 12 valid digits  is good enough usually if no extreme accuracy or no extreme number of successive arithmetic operations is required   Infinite test  import random from decimal import Decimal for x in iter random random  None               Verify FOREVER that rounding is fixed  -      assert float repr x      x                  Reversible repr   conversion      assert float Decimal repr x       x     assert len repr round x  10     lt   12        Smart decimal places in repr   after round      if x  gt   0 1                                 Implicit rounding to 12 significant digits         assert str x     repr round x  12       by str   is good enough for small errors          y   1000   x                               Decimal type is excessive for shopping         assert str y     repr round y  12 - 3      in a supermaket with Python 2 7   -   Documentation See the Release notes Python 2 7 - Other Language Changes the fourth paragraph   Conversions between floating-point numbers and strings are now correctly rounded on most platforms  These conversions occur in many different places  str   on floats and complex numbers  the float and complex constructors  numeric formatting  serializing and de-serializing floats and complex numbers using the marshal  pickle and json modules  parsing of float and imaginary literals in Python code  and Decimal-to-float conversion  Related to this  the repr   of a floating-point number x now returns a result based on the shortest decimal string that   s guaranteed to round back to x under correct rounding  with round-half-to-even rounding mode   Previously it gave a string based on rounding x to 17 decimal digits   The related issue  More information  The formatting of float before Python 2 7 was similar to the current numpy float64  Both types use the same 64 bit IEEE 754 double precision with 52 bit mantissa  A big difference is that np float64   repr   is formatted frequently with an excessive decimal number so that no bit can be lost  but no valid IEEE 754 number exists between 13 949999999999999 and 13 950000000000001  The result is not nice and the conversion repr float number as string   is not reversible with numpy  On the other hand  float   repr   is formatted so that every digit is important  the sequence is without gaps and the conversion is reversible  Simply  If you perhaps have a numpy float64 number  convert it to normal float in order to be formatted for humans  not for numeric processors  otherwise nothing more is necessary with Python 2 7

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Nobody here seems to have mentioned it yet  so let me give an example in Python 3 6 s f-string template-string format  which I think is beautifully neat    gt  gt  gt  f  a  2f     It works well with longer examples too  with operators and not needing parens    gt  gt  gt  print f Completed in  time time   - start  2f s

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It s doing exactly what you told it to do and is working correctly  Read more about floating point confusion and maybe try decimal objects instead

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You can use format operator for rounding the value up to 2 decimal places in python   print format 14 4499923    2f       output is 14 45

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If you want to handle money  use python decimal module from decimal import Decimal  ROUND HALF UP    amount can be integer  string  tuple  float  or another Decimal object def to money amount  - gt  Decimal      money   Decimal amount  quantize Decimal   00    rounding ROUND HALF UP      return money

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You can modify the output format    gt  gt  gt  a   13 95  gt  gt  gt  a 13 949999999999999  gt  gt  gt  print    2f    a 13 95

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You can modify the output format    gt  gt  gt  a   13 95  gt  gt  gt  a 13 949999999999999  gt  gt  gt  print    2f    a 13 95

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I feel that the simplest approach is to use the format   function   For example   a   13 949999999999999 format a    2f    13 95   This produces a float number as a string rounded to two decimal points

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With Python  lt  3  e g  2 6 or 2 7   there are two ways to do so     Option one  older method string      9f    numvar    Option two  note     before the   9f   newer method string       9f   format numvar    But note that for Python versions above 3  e g  3 2 or 3 3   option two is preferred   For more information on option two  I suggest this link on string formatting from the Python documentation   And for more information on option one  this link will suffice and has information on the various flags   Reference  Convert floating point number to a certain precision  and then copy to string

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I feel that the simplest approach is to use the format   function   For example   a   13 949999999999999 format a    2f    13 95   This produces a float number as a string rounded to two decimal points

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Nobody here seems to have mentioned it yet  so let me give an example in Python 3 6 s f-string template-string format  which I think is beautifully neat    gt  gt  gt  f  a  2f     It works well with longer examples too  with operators and not needing parens    gt  gt  gt  print f Completed in  time time   - start  2f s

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You are running into the old problem with floating point numbers that not all numbers can be represented exactly  The command line is just showing you the full floating point form from memory   With floating point representation  your rounded version is the same number  Since computers are binary  they store floating point numbers as an integer and then divide it by a power of two so 13 95 will be represented in a similar fashion to 125650429603636838  2  53    Double precision numbers have 53 bits  16 digits  of precision and regular floats have 24 bits  8 digits  of precision  The floating point type in Python uses double precision to store the values   For example    gt  gt  gt  125650429603636838  2  53  13 949999999999999   gt  gt  gt  234042163  2  24  13 949999988079071   gt  gt  gt  a   13 946  gt  gt  gt  print a  13 946  gt  gt  gt  print    2f    a  13 95  gt  gt  gt  round a 2  13 949999999999999  gt  gt  gt  print    2f    round a  2   13 95  gt  gt  gt  print     2f   format a   13 95  gt  gt  gt  print     2f   format round a  2    13 95  gt  gt  gt  print     15f   format round a  2    13 949999999999999   If you are after only two decimal places  to display a currency value  for example   then you have a couple of better choices    Use integers and store values in cents  not dollars and then divide by 100 to convert to dollars  Or use a fixed point number like decimal

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It s doing exactly what you told it to do and is working correctly  Read more about floating point confusion and maybe try decimal objects instead

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Use combination of Decimal object and round   method   Python 3 7 3  gt  gt  gt  from decimal import Decimal  gt  gt  gt  d1   Decimal  13 949999999999999    define a Decimal  gt  gt  gt  d1  Decimal  13 949999999999999289457264239899814128875732421875    gt  gt  gt  d2   round d1  2    round to 2 decimals  gt  gt  gt  d2 Decimal  13 95

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Use  print    2f   format a    instead of  print  0  2f   format a    Because the latter may lead to output errors when trying to output multiple variables  see comments

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As  Matt pointed out  Python 3 6 provides f-strings  and they can also use nested parameters   value   2 34558 precision   2 width   4  print f result   value  width   precision f      which will display result  2 35

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We multiple options to do that   Option 1  x   1 090675765757 g   float  quot    2f  quot  format x   print g   Option 2  The built-in round   supports Python 2 7 or later  x   1 090675765757 g    round x  2  print g

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You can modify the output format    gt  gt  gt  a   13 95  gt  gt  gt  a 13 949999999999999  gt  gt  gt  print    2f    a 13 95

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The method I use is that of string slicing  It s relatively quick and simple   First  convert the float to a string  the choose the length you would like it to be   float   str float   5    In the single line above  we ve converted the value to a string  then kept the string only to its first four digits or characters  inclusive    Hope that helps

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The built-in round   works just fine in Python 2 7 or later   Example    gt  gt  gt  round 14 22222223  2  14 22   Check out the documentation

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orig float   232569   16000 0      14 5355625   short float   float     2f   format orig float         14 54

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Most numbers cannot be exactly represented in floats  If you want to round the number because that s what your mathematical formula or algorithm requires  then you want to use round  If you just want to restrict the display to a certain precision  then don t even use round and just format it as that string   If you want to display it with some alternate rounding method  and there are tons  then you need to mix the two approaches     gt  gt  gt     2f    3 14159  3 14   gt  gt  gt     2f    13 9499999  13 95    And lastly  though perhaps most importantly  if you want exact math then you don t want floats at all  The usual example is dealing with money and to store  cents  as an integer

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Most numbers cannot be exactly represented in floats  If you want to round the number because that s what your mathematical formula or algorithm requires  then you want to use round  If you just want to restrict the display to a certain precision  then don t even use round and just format it as that string   If you want to display it with some alternate rounding method  and there are tons  then you need to mix the two approaches     gt  gt  gt     2f    3 14159  3 14   gt  gt  gt     2f    13 9499999  13 95    And lastly  though perhaps most importantly  if you want exact math then you don t want floats at all  The usual example is dealing with money and to store  cents  as an integer

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The answers I saw didn t work with the float 52 15  case  After some tests  there is the solution that I m using  import decimal          def value to decimal value  decimal places       decimal getcontext   rounding   decimal ROUND HALF UP    define rounding method     return decimal Decimal str float value    quantize decimal Decimal  1e-    format decimal places      The conversion of the  value  to float and then string is very important  that way   value  can be of the type float  decimal  integer or string   Hope this helps anyone

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You are running into the old problem with floating point numbers that not all numbers can be represented exactly  The command line is just showing you the full floating point form from memory   With floating point representation  your rounded version is the same number  Since computers are binary  they store floating point numbers as an integer and then divide it by a power of two so 13 95 will be represented in a similar fashion to 125650429603636838  2  53    Double precision numbers have 53 bits  16 digits  of precision and regular floats have 24 bits  8 digits  of precision  The floating point type in Python uses double precision to store the values   For example    gt  gt  gt  125650429603636838  2  53  13 949999999999999   gt  gt  gt  234042163  2  24  13 949999988079071   gt  gt  gt  a   13 946  gt  gt  gt  print a  13 946  gt  gt  gt  print    2f    a  13 95  gt  gt  gt  round a 2  13 949999999999999  gt  gt  gt  print    2f    round a  2   13 95  gt  gt  gt  print     2f   format a   13 95  gt  gt  gt  print     2f   format round a  2    13 95  gt  gt  gt  print     15f   format round a  2    13 949999999999999   If you are after only two decimal places  to display a currency value  for example   then you have a couple of better choices    Use integers and store values in cents  not dollars and then divide by 100 to convert to dollars  Or use a fixed point number like decimal

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Use  print    2f   format a    instead of  print  0  2f   format a    Because the latter may lead to output errors when trying to output multiple variables  see comments

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TLDR    The rounding problem of input   output has been solved definitively by Python 2 7 0 and 3 1  A correctly rounded number can be reversibly converted back and forth  str - gt  float   - gt  repr   - gt  float       or Decimal - gt  float - gt  str - gt  Decimal A Decimal type is not necessary for storage anymore    Naturally  it can be necessary to round a result of addition or subtraction of rounded numbers to eliminate the accumulated last bit errors  An explicit Decimal arithmetic can be still handy  but a conversion to string by str    that is with rounding to 12 valid digits  is good enough usually if no extreme accuracy or no extreme number of successive arithmetic operations is required   Infinite test  import random from decimal import Decimal for x in iter random random  None               Verify FOREVER that rounding is fixed  -      assert float repr x      x                  Reversible repr   conversion      assert float Decimal repr x       x     assert len repr round x  10     lt   12        Smart decimal places in repr   after round      if x  gt   0 1                                 Implicit rounding to 12 significant digits         assert str x     repr round x  12       by str   is good enough for small errors          y   1000   x                               Decimal type is excessive for shopping         assert str y     repr round y  12 - 3      in a supermaket with Python 2 7   -   Documentation See the Release notes Python 2 7 - Other Language Changes the fourth paragraph   Conversions between floating-point numbers and strings are now correctly rounded on most platforms  These conversions occur in many different places  str   on floats and complex numbers  the float and complex constructors  numeric formatting  serializing and de-serializing floats and complex numbers using the marshal  pickle and json modules  parsing of float and imaginary literals in Python code  and Decimal-to-float conversion  Related to this  the repr   of a floating-point number x now returns a result based on the shortest decimal string that   s guaranteed to round back to x under correct rounding  with round-half-to-even rounding mode   Previously it gave a string based on rounding x to 17 decimal digits   The related issue  More information  The formatting of float before Python 2 7 was similar to the current numpy float64  Both types use the same 64 bit IEEE 754 double precision with 52 bit mantissa  A big difference is that np float64   repr   is formatted frequently with an excessive decimal number so that no bit can be lost  but no valid IEEE 754 number exists between 13 949999999999999 and 13 950000000000001  The result is not nice and the conversion repr float number as string   is not reversible with numpy  On the other hand  float   repr   is formatted so that every digit is important  the sequence is without gaps and the conversion is reversible  Simply  If you perhaps have a numpy float64 number  convert it to normal float in order to be formatted for humans  not for numeric processors  otherwise nothing more is necessary with Python 2 7

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The method I use is that of string slicing  It s relatively quick and simple   First  convert the float to a string  the choose the length you would like it to be   float   str float   5    In the single line above  we ve converted the value to a string  then kept the string only to its first four digits or characters  inclusive    Hope that helps

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We multiple options to do that   Option 1  x   1 090675765757 g   float  quot    2f  quot  format x   print g   Option 2  The built-in round   supports Python 2 7 or later  x   1 090675765757 g    round x  2  print g

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The Python tutorial has an appendix called Floating Point Arithmetic  Issues and Limitations  Read it  It explains what is happening and why Python is doing its best  It has even an example that matches yours  Let me quote a bit     gt  gt  gt  0 1 0 10000000000000001       you may be tempted to use the round     function to chop it back to the single   digit you expect  But that makes no   difference    gt  gt  gt  round 0 1  1  0 10000000000000001       The problem is that the binary   floating-point value stored for    0 1      was already the best possible binary   approximation to 1 10  so trying to   round it again can   t make it better    it was already as good as it gets       Another consequence is that since 0 1   is not exactly 1 10  summing ten   values of 0 1 may not yield exactly   1 0  either    gt  gt  gt  sum   0 0  gt  gt  gt  for i in range 10           sum    0 1      gt  gt  gt  sum 0 99999999999999989    One alternative and solution to your problems would be using the decimal module

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You can modify the output format    gt  gt  gt  a   13 95  gt  gt  gt  a 13 949999999999999  gt  gt  gt  print    2f    a 13 95

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Try the code below    gt  gt  gt  a   0 99334  gt  gt  gt  a   int  a   100    0 5    100 0   Adding 0 5 rounds it up  gt  gt  gt  print a 0 99

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In Python 2 7   a   13 949999999999999 output   float   0 2f  a  print output

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float number   12 234325335563 round float number  2   This will return  12 23  round function takes two arguments  Number to be rounded and the number of decimal places to be returned Here i returned 2 decimal places

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If you want to handle money  use python decimal module from decimal import Decimal  ROUND HALF UP    amount can be integer  string  tuple  float  or another Decimal object def to money amount  - gt  Decimal      money   Decimal amount  quantize Decimal   00    rounding ROUND HALF UP      return money

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Use combination of Decimal object and round   method   Python 3 7 3  gt  gt  gt  from decimal import Decimal  gt  gt  gt  d1   Decimal  13 949999999999999    define a Decimal  gt  gt  gt  d1  Decimal  13 949999999999999289457264239899814128875732421875    gt  gt  gt  d2   round d1  2    round to 2 decimals  gt  gt  gt  d2 Decimal  13 95

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What about a lambda function like this   arred   lambda x n   x  10  n   1  10  n    This way you could just do    arred 3 141591657 2    and get   3 14

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With Python  lt  3  e g  2 6 or 2 7   there are two ways to do so     Option one  older method string      9f    numvar    Option two  note     before the   9f   newer method string       9f   format numvar    But note that for Python versions above 3  e g  3 2 or 3 3   option two is preferred   For more information on option two  I suggest this link on string formatting from the Python documentation   And for more information on option one  this link will suffice and has information on the various flags   Reference  Convert floating point number to a certain precision  and then copy to string

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For fixing the floating point in type-dynamic languages such as Python and JavaScript  I use this technique    For example  a   70000 b   0 14 c   a   b  print c   Prints 980 0000000002   Try to fix c   int c   10000  100000 print c   Prints 980   You can also use Decimal as following   from decimal import   getcontext   prec   6 Decimal 1    Decimal 7    Results in 6 precision - gt  Decimal  0 142857    getcontext   prec   28 Decimal 1    Decimal 7    Results in 28 precision - gt  Decimal  0 1428571428571428571428571429

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In Python 2 7   a   13 949999999999999 output   float   0 2f  a  print output

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The Python tutorial has an appendix called Floating Point Arithmetic  Issues and Limitations  Read it  It explains what is happening and why Python is doing its best  It has even an example that matches yours  Let me quote a bit     gt  gt  gt  0 1 0 10000000000000001       you may be tempted to use the round     function to chop it back to the single   digit you expect  But that makes no   difference    gt  gt  gt  round 0 1  1  0 10000000000000001       The problem is that the binary   floating-point value stored for    0 1      was already the best possible binary   approximation to 1 10  so trying to   round it again can   t make it better    it was already as good as it gets       Another consequence is that since 0 1   is not exactly 1 10  summing ten   values of 0 1 may not yield exactly   1 0  either    gt  gt  gt  sum   0 0  gt  gt  gt  for i in range 10           sum    0 1      gt  gt  gt  sum 0 99999999999999989    One alternative and solution to your problems would be using the decimal module

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Try the code below    gt  gt  gt  a   0 99334  gt  gt  gt  a   int  a   100    0 5    100 0   Adding 0 5 rounds it up  gt  gt  gt  print a 0 99

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Most numbers cannot be exactly represented in floats  If you want to round the number because that s what your mathematical formula or algorithm requires  then you want to use round  If you just want to restrict the display to a certain precision  then don t even use round and just format it as that string   If you want to display it with some alternate rounding method  and there are tons  then you need to mix the two approaches     gt  gt  gt     2f    3 14159  3 14   gt  gt  gt     2f    13 9499999  13 95    And lastly  though perhaps most importantly  if you want exact math then you don t want floats at all  The usual example is dealing with money and to store  cents  as an integer

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You can use format operator for rounding the value up to 2 decimal places in python   print format 14 4499923    2f       output is 14 45

[python] Limiting floats to two decimal points

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