Python Decimal to string产生奇怪的科学记数法

Question

I am dealing with a bug where applying the str function to an instance of decimal.Decimal gives me the string '0E-1000' . I expected that str applied to a Decimal would always give me a string of the form -?[0-9]+(\\.[0-9]+) , which is what I want.

Firstly, if I understand correctly, the scientific notation '0E-1000' represents 0 x 10^-1000, ie zero. Why am I getting this particular representation of zero? Why not '0E-42' , which is the same?

Secondly, I cannot manually construct a Decimal which reproduces this bug. The buggy Decimal instance comes from an external source. The expression str(Decimal(0)) evaluates to '0' in the REPL. How can I construct an instance d of Decimal for which str(d) evaluates to '0E-1000' ?

EDIT: Thirdly, how can I convert an arbitrary Decimal instance to a string in, you know, decimal notation?

Answer 1

If you want to reproduce your decimal, just construct it from the string:

>>> d=decimal.Decimal("0E-1000")
>>> str(d)
'0E-1000'

I believe the difference is the difference between 0 and 0.00000 (or in your case 1000 zeros), which is the accuracy. This could be significant in scientific situations, where rounding etc. is controlled by the precision of the operands. If you want to make printing consistent, use decimal.Decimal.normalize :

>>> d=decimal.Decimal("0E-1000")
>>> d
Decimal('0E-1000')
>>> d.normalize()
Decimal('0')
>>> str(d.normalize())
'0'