jackiekazil/rounding_decimals.md

See here for an alternative using __format__

I think you have to use the Decimal() with strings ?
Because
Decimal(1.1)+Decimal(2.2) == 3.300000000000000266453525910
While
Decimal(repr(1.1))+Decimal(repr(2.2)) == 3.3

Or am I wrong?

Decimal(float) will give you the decimal representation of a floating point number. What you're seeing is the entire raison d'etre for Decimals; floats are binary approximations of (supposedly really large) numbers, converting them to Decimal (or trying to round them etc.) will expose that approximation, and if you're not aware of those internals you'll run into these kinds of suprises.

See for example https://docs.python.org/3/tutorial/floatingpoint.html

I don't think rounding by setting the precision is viable as it takes into account the digits before the decimal point as well as after (hence why set to 3 and not 2). In you example if you do:

from decimal import getcontext, Decimal
getcontext().prec = 3
output = Decimal(160.0)/Decimal(7)
print output
22.9

Which I don't think is what you want? You can of course set prec to 4, but that's not really a solution.

if i'll write
v= Decimal(x)
x is a float() type ,then can i use round(v,2)?

@rpxz if you have added the line above it that says:
from decimal import Decimal

Hello, thank you very much for sharing.
I found a strange result, maybe it is a bug in the decimal module. The code is shown below.

>>>from decimal import Decimal, ROUND_HALF_UP
>>>val = Decimal(1.45)
>>>Decimal(val.quantize(Decimal('0.1'), rounding=ROUND_HALF_UP))

Decimal('1.4')

The correct result should be Decimal('1.5').
By the way, I am using Python 3.5.

You forgot to pass 1.45 as a string:

Python 3.5.4rc1 (default, Jul 25 2017, 08:53:34) 
[GCC 6.4.0 20170704] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from decimal import Decimal, ROUND_HALF_UP
>>> val = Decimal('1.45')
>>> Decimal(val.quantize(Decimal('0.1'), rounding=ROUND_HALF_UP))
Decimal('1.5')
>>> Decimal(1.45) - Decimal('1.45')
Decimal('-4.440892098500626161694526672E-17')

Which is mentioned above in https://gist.github.com/jackiekazil/6201722#gistcomment-1641922

https://www.youtube.com/watch?v=l1coJkTxhBY

if anyone could understand this videos can you please write for me the steps and the code so I can type it in paython interpreter
I will be very thankfull

nice 👍

3a. Round decimals by setting precision without Decimal

to round float to 3 significant figures without dealing with Decimal module:

>>> '%s' % float('%.3g' % 3.141592654)
'3.14'

%s required to prevent python from printing float in e- scientific notation

Ref: https://stackoverflow.com/questions/3410976/how-to-round-a-number-to-significant-figures-in-python

for Python 3

Depending on the number you want to round
Kindly use, Example

The codes start below

a = 16 / 7
print ("%.1f" % a)

Explaining

#The '1 explains where it should starts from
just after the decimal point.
#The 'a' represents the value you assigned it to
If you want it to round on the second, use 2
Like this ----below is the code

print ("%.2f" % a)

how to get 3.25, 3.27, 3.29 to be considered as 3.25 and 3.20, 3.22, 3.24 to be considered as 3.20 ? any advice.

Decimal has a quite high impact on performances:

In [12]: timeit.timeit("round(7.325, 2)")
Out[12]: 0.39438656000129413

In [9]: timeit.timeit("from decimal import Decimal, ROUND_DOWN;round(Decimal('7.325'), 2)")
Out[9]: 0.9643819720076863

In [21]: timeit.timeit("float('%.2f' % 7.325)")
Out[21]: 0.3827699579996988

@Mec-iS While Decimal is indeed slower, I believe your example is not totally correct. You measure imports together with initializing Decimal object. IMO timeit.timeit(stmt="round(d, 2)", setup="from decimal import Decimal, ROUND_DOWN;d=Decimal('7.325')") would be closer analog of rounding floats.

Slow but correct, I choose Decimal .

Money class method from py-moneyed:

def round(self, ndigits=0):
    """
    Rounds the amount using the current ``Decimal`` rounding algorithm.
    """
    if ndigits is None:
        ndigits = 0
    return self.__class__(
        amount=self.amount.quantize(Decimal('1e' + str(-ndigits))),
        currency=self.currency
    )

python has a built in round function that allows you to specify the number of decimals to truncate too. See https://stackoverflow.com/questions/455612/limiting-floats-to-two-decimal-points

A