Limiting floats to two decimal points

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,

>>> 125650429603636838/(2**53)
13.949999999999999

>>> 234042163/(2**24)
13.949999988079071

>>> a = 13.946
>>> print(a)
13.946
>>> print("%.2f" % a)
13.95
>>> round(a,2)
13.949999999999999
>>> print("%.2f" % round(a, 2))
13.95
>>> print("{:.2f}".format(a))
13.95
>>> print("{:.2f}".format(round(a, 2)))
13.95
>>> 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:

1. Use integers and store values in cents, not dollars and then divide by 100 to convert to dollars.
2. Or use a fixed point number like decimal.

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.)

>>> "%.2f" % 3.14159
'3.14'
>>> "%.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.

float_number = 12.234325335563
round(float_number, 2)

This will return;

12.23

Explanation:

round function takes two arguments; Number to be rounded and the number of decimal places to be returned.Here i returned 2 decimal places.

You can modify the output format:

>>> a = 13.95
>>> a
13.949999999999999
>>> print "%.2f" % a
13.95

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

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

We multiple options to do that : Option 1:

x = 1.090675765757
g = float("{:.2f}".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)

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:

>>> 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:

>>> 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:

>>> sum = 0.0
>>> for i in range(10):
...     sum += 0.1
...
>>> sum
0.99999999999999989

One alternative and solution to your problems would be using the decimal module.

Use combination of Decimal object and round() method.

Python 3.7.3
>>> from decimal import Decimal
>>> d1 = Decimal (13.949999999999999) # define a Decimal
>>> d1 
Decimal('13.949999999999999289457264239899814128875732421875')
>>> d2 = round(d1, 2) # round to 2 decimals
>>> d2
Decimal('13.95')

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.

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)
>>> round_float(3.1415926)
Decimal('3.14')
>>> round_float(3.1445926)
Decimal('3.14')
>>> round_float(3.1455926)
Decimal('3.15')
>>> round_float(3.1455926, rt_str=True)
'3.15'
>>> str(round_float(3.1455926))
'3.15'

The simple solution is here

value = 5.34343
rounded_value = round(value, 2) # 5.34

It's simple like 1,2,3:

1. 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')

2. 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)

3. upvote this answer :)

PS: critique of others: formatting is not rounding.

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

Here is the Simple Solution Using format Function.

float(format(num, '.2f'))

NOTE: We are converting numbers to float because format method is returning string.

lambda x,n:int(x*10^n+.5)/10^n has worked for me for many years in many languages.

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) -> Decimal:
    money = Decimal(amount).quantize(Decimal('.00'), rounding=ROUND_HALF_UP)
    return money

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.

Just use this function and pass bytes as an input to it:

def getSize(bytes):
    kb = round(bytes/1024, 4)
    mb = round(kb/1024, 4)
    gb = round(mb/1024, 4)
    if(gb > 1):
        return str(gb)+" GB"
    elif(mb > 1):
        return str(mb)+" MB"
    else:
        return str(kb)+" KB"

This is the easiest way I could get to convert the data size from bytes to KB,MB or GB dynamically

One-liner function to print percentage:

k - the numerator

n - the denominator

'%.2f' - means you want a precision of 2 decimal places

*100 - turns the number from a decimal to a percentage

   percentage = lambda k, n: '%.2f' % (k/n*100)

   - equivalent to-

   def percentage(k,n):
       return '%.2f' % (k/n*100)

percentage(1,3)

output -> '33.33'