[Python-Dev] Two proposed changes to float formatting (original) (raw)

Mark Dickinson dickinsm at gmail.com
Sun Apr 26 21:19:20 CEST 2009

On Sun, Apr 26, 2009 at 8:11 PM, Scott David Daniels <Scott.Daniels at acm.org> wrote:

As a user of Idle, I would not like to see the change you seek of having %f stay full-precision.  When a number gets too long to print on a single line, the wrap depends on the current window width, and is calculated dynamically.  One section of the display with a 8000 -digit (100-line) text makes Idle slow to scroll around in.  It is too easy for numbers to go massively positive in a bug.

I see your point. Since we're talking about floats, thought, there should never be more than 316 characters in a '%f' % x: the largest float is around 1.8e308, giving 308 digits before the point, 6 after, a decimal point, and possibly a minus sign. (Assuming that your platform uses IEEE 754 doubles.)

However, this is, I agree, a problem.  Since all of these numbers should end in a massive number of zeroes

But they typically don't end in zeros (except the six zeros following the point), because they're stored in binary rather than decimal. For example:

int(1e308) 100000000000000001097906362944045541740492309677311846336810682903157585404911491537163328978494688899061249669721172515611590283743140088328307009198146046031271664502933027185697489699588559043338384466165001178426897626212945177628091195786707458122783970171784415105291802893207873272974885715430223118336

Mark

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