[New-bugs-announce] [issue25839] negative zero components are ignored in complex number literals

[Mark Lundeberg]

New submission from Mark Lundeberg:

Although -0.0 and +0.0 compare as equal using the == operator, they are distinct floating point numbers and in some cases behave differently. (See more information on the wikipedia article "Signed zero".) The distinction between +0.0 and -0.0 is most important in complex arithmetic, for example it is conventional and useful that sqrt(-1+0i) ==> +i and sqrt(-1-0i) ==> -i. Python currently allows the floating point number -0.0 to be entered as a literal:

>>> -0.0
-0.0

Complex floating point numbers in python also can hold negative zero components, as shown in their repr()

>>> -(1+0j)
(-1-0j)

However they cannot be input directly as literals; it is currently necessary to use the above construction. Unfortunately the output of the repr() cannot be used as a string literal to obtain the same number:

>>> (-1-0j)
(-1+0j)

except, in contrast:

>>> complex('-1-0j')
(-1-0j)


The literal -1-0j should yield a complex number with negative zero imaginary part. Note also that complex literals with negative zero real parts have the same bug, e.g. -0+1j is not the same as -(0-1j)

----------
components: Interpreter Core
messages: 256209
nosy: Mark Lundeberg
priority: normal
severity: normal
status: open
title: negative zero components are ignored in complex number literals
type: behavior
versions: Python 2.7, Python 3.4

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25839>
_______________________________________