Force calculation result as decimal

[vercetty92]

Hi folks,

I come here to ask you a quick question

I am a noob in python and I have a so simple problem. I looked at several python documentations, but I think my poor basic knowlegde of python doesn't permit me to find what I am looking for....so I came here^^

I am not developping a python script, but simply using the calculation feature of ptyhon, which is more powerfull than the one on script shell.
I'm doing it by calling "python -c" from linux CLI

#python -c "print 0.0000006 + 0.0000008"
1.4e-06

question is : how do I force python to have a result in decimal (example 0.xxxxxxxxxx)

Thanks a lot in advance

[nilamo]

If you want a number formatted a certain way, then you probably want to use string formatting. Or the decimal module, depending on how exact you want it:

C:\Users\nilamo>python -c "print('{0:.10f}'.format(0.0000006 + 0.0000008))"
0.0000014000

C:\Users\nilamo>python -c "from decimal import Decimal; print(Decimal(0.0000006 + 0.0000008))"
0.000001399999999999999936647356556240762159859514213167130947113037109375

C:\Users\nilamo>python -c "from decimal import Decimal; print(Decimal(0.0000006) + Decimal(0.0000008))"
0.000001399999999999999936647356556

[vercetty92]

Hi Nilamo,

Thanks a lot for your answer.

Your first command works fine, for the 2 others it returns :

# python -c "from decimal import Decimal; print(Decimal(0.0000006) + Decimal(0.0000008))"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib64/python2.6/decimal.py", line 649, in __new__
    "First convert the float to a string")

is there no command to simply display the result that automatically stick to the number with the higher number of digit?

thx a lot

[scidam]

To avoid errors of floating point object representation in memory, it is better to pass strings to Decimal class, e.g.
python -c "from decimal import Decimal; print(Decimal('0.0000006') + Decimal('0.0000008'))". This likely should work in python2.6.
@vercetty92, why did you are still using Python 2.6? Constructor of Decimal class in current versions of Python, e.g. Python 3.7, could process floats directly (without errors as in your example).

[vercetty92]

Hi Scidam,
this solution is perfect to me thx a lot dude!

I am using python 2.6 because this is the version redhat provides by defaut (2.6 on el6 & 2.7 on el7). Of course we can enable the software-collection repository and install python3, but we never really had this need (the destination server is not really a development server so we avoid to install unecessary thing^^)

thx