[Python-Dev] Proposal: make float.str identical tofloat__repr__ in Python 3.2 (original) (raw)

Robert Brewer fumanchu at aminus.org
Thu Jul 29 23:37:34 CEST 2010

Mark Dickinson wrote:

Now that we've got the short float repr in Python, there's less value in having float.str truncate to 12 significant digits (as it currently does). For Python 3.2, I propose making float.str use the same algorithm as float.repr for its output (and similarly for complex).

Apart from simplifying the internals a little bit, one nice feature of this change is that it removes the differences in formatting between printing a float and printing a container of floats: >>> l = [1/3, 1/5, 1/7] >>> print(l) [0.3333333333333333, 0.2, 0.14285714285714285] >>> print(l[0], l[1], l[2]) 0.333333333333 0.2 0.142857142857 Any thoughts or comments on this? There's a working patch at http://bugs.python.org/issue9337

Python 2.5.4 (r254:67916, Jan 20 2010, 21:44:03)

float("0.142857142857") * 7 0.99999999999899991 float("0.14285714285714285") * 7 1.0

I've made a number of tools in the past that needed to round-trip a float through a string and back. I was under the impression that floats needed 17 decimal digits to avoid losing precision. How does one do that efficiently if neither str nor repr return 17 digits?

Robert Brewer fumanchu at aminus.org

More information about the Python-Dev mailing list