[python] Python 3 Float Decimal Points/Precision

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().

The comments state the objective is to print to 2 decimal places.

There's a simple answer for Python 3:

>>> num=3.65
>>> "The number is {:.2f}".format(num)
'The number is 3.65'

or equivalently with f-strings (Python 3.6+):

>>> num = 3.65
>>> f"The number is {num:.2f}"
'The number is 3.65'

As always, the float value is an approximation:

>>> "{}".format(num)
'3.65'
>>> "{:.10f}".format(num)
'3.6500000000'
>>> "{:.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.

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)

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!

The simple way to do this is by using the round buit-in.

round(2.6463636263,2) would be displayed as 2.65.