(Iron)Python formatting issue with modulo operator & "negative zero"

Question

Today i noticed following issue on IronPython2.7:

When formatting a format_string like so, i get a "negativ zero". I get the same result if i use Python2.7 or Python3.4 instead of IronPython.

>>> "%.2f" % -0.004
'-0.00'

Then i realized, that i can get rid of the negativ zero by passing two arguments to the format string like so:

>>> "%s%.2f" % ('x', -0.004)
'x0.00'

'x' is a random character. So, i format another string before the float value and the minus disappears. That does not work with Python2.7 and Python3.4 though, where i get:

>>> "%s%.2f" % ('x', -0.004)
'x-0.00'

Does anybody know what's going on here?

What is the purpose of the formatted "negativ zero" at all?

Answer 1

(edited to take @MarkDikinson comment into account)

You can format the number first, then doing the printf-like formatting:

"%.2f" % (round(-0.004, 2)+0)

The +0 is there to remove the negative zero sign.

round can also take a ndigits argument, to specify how many digits you need for the rounding of the number itself (not talking about display, which is handled by "%.2f").