Python 3 Float Decimal Points Precision

Question

I am reading a text file with floating point numbers  all with either 1 or 2 decimal points  I am using float   to convert a line into a float  and raising a ValueError if that fails  I am storing all floats in a list  When printing it out  I d like to print it out as a 2 decimal places floating point   Assume I have a text file with the numbers -3 65  9 17  1  I read each one  and once I convert them to float and append them to a list  Now in Python 2  calling float -3 65  returns -3 65  In Python 3 however  float -3 65  returns-3 6499999999999999  which loses its precision   I want to print the list of floats   -3 6499999999999999  9 1699999999999999  1 0  with 2 decimal points only  Doing something along the lines of    1f    round n  1  would return a string  How can I return a list of all two decimal points of floats  and not strings  So far  I rounded it using  round num  2  for num in list  but would need to set the decimal points   precision instead of round

User · Answer

Try to understand through this below function using python3

def floating_decimals(f_val, dec):
    prc = "{:."+str(dec)+"f}" #first cast decimal as str
    print(prc) #str format output is {:.3f}
    return prc.format(f_val)


print(floating_decimals(50.54187236456456564, 3))

Output is : 50.542

Hope this helps you!

User · Answer

The comments state the objective is to print to 2 decimal places    There s a simple answer for Python 3    gt  gt  gt  num 3 65  gt  gt  gt   The number is    2f   format num   The number is 3 65    or equivalently with f-strings  Python 3 6      gt  gt  gt  num   3 65  gt  gt  gt  f The number is  num  2f    The number is 3 65    As always  the float value is an approximation    gt  gt  gt       format num   3 65   gt  gt  gt      10f   format num   3 6500000000   gt  gt  gt      20f   format num   3 64999999999999991118    I think most use cases will want to work with floats and then only print to a specific precision   Those that want the numbers themselves to be stored to exactly 2 decimal digits of precision  I suggest use the decimal type  More reading on floating point precision for those that are interested

User · Answer

Try this   num   input  Please input your number      num   float   0 2f     num    print num    I believe this is a lot simpler  For 1 decimal place use  0 1f  For 2 decimal places use  0 2f and so on   Or  if you want to reduce it all to 2 lines   num   float   0 2f     float input  Please input your number        print num

User · Answer

In a word  you can t   3 65 cannot be represented exactly as a float  The number that you re getting is the nearest number to 3 65 that has an exact float representation   The difference between  older   Python 2 and 3 is purely due to the default formatting   I am seeing the following both in Python 2 7 3 and 3 3 0   In  1   3 65 Out 1   3 65  In  2      20f    3 65 Out 2    3 64999999999999991118    For an exact decimal datatype  see decimal Decimal

User · Answer

The simple way to do this is by using the round buit-in     round 2 6463636263 2  would be displayed as 2 65

[python] Python 3 Float Decimal Points/Precision

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