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Merged revisions 73656,73658,73663,73666 via svnmerge from

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  r73656 | mark.dickinson | 2009-06-29 00:08:40 +0200 (Mo, 29 Jun 2009) | 1 line

  Fix description of range_length_obj
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  r73658 | raymond.hettinger | 2009-06-29 00:30:13 +0200 (Mo, 29 Jun 2009) | 1 line

  Small doc fix-ups to floatingpoint.rst.  More are forthcoming.
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  r73663 | raymond.hettinger | 2009-06-29 01:21:38 +0200 (Mo, 29 Jun 2009) | 1 line

  Clean-up floating point tutorial.
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  r73666 | alexandre.vassalotti | 2009-06-29 03:13:41 +0200 (Mo, 29 Jun 2009) | 2 lines

  Make b64encode raises properly a TypeError when altchars is not bytes.
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This commit is contained in:
Georg Brandl 2009-08-13 08:47:18 +00:00
parent 98e472d7fb
commit 7d1e88063c
3 changed files with 10 additions and 11 deletions
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10
Doc/tutorial/floatingpoint.rst
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@ -82,7 +82,7 @@ values share the same approximation, any one of them could be displayed
while still preserving the invariant ``eval(repr(x)) == x``.
Historically, the Python prompt and built-in :func:`repr` function would chose
the one with 17 significant digits, ``0.10000000000000001``, Starting with
the one with 17 significant digits, ``0.10000000000000001``. Starting with
Python 3.1, Python (on most systems) is now able to choose the shortest of
these and simply display ``0.1``.
@ -123,9 +123,9 @@ Also, since the 0.1 cannot get any closer to the exact value of 1/10 and
Though the numbers cannot be made closer to their intended exact values,
the :func:`round` function can be useful for post-rounding so that results
have inexact values that are comparable to one another::
with inexact values become comparable to one another::
>>> round(.1 + .1 + .1, 1) == round(.3, 1)
>>> round(.1 + .1 + .1, 10) == round(.3, 10)
True
Binary floating-point arithmetic holds many surprises like this. The problem
@ -137,7 +137,7 @@ As that says near the end, "there are no easy answers." Still, don't be unduly
wary of floating-point! The errors in Python float operations are inherited
from the floating-point hardware, and on most machines are on the order of no
more than 1 part in 2\*\*53 per operation. That's more than adequate for most
tasks, but you do need to keep in mind that it's not decimal arithmetic, and
tasks, but you do need to keep in mind that it's not decimal arithmetic and
that every float operation can suffer a new rounding error.
While pathological cases do exist, for most casual use of floating-point
@ -165,7 +165,7 @@ fraction::
>>> x = 3.14159
>>> x.as_integer_ratio()
(3537115888337719L, 1125899906842624L)
(3537115888337719, 1125899906842624)
Since the ratio is exact, it can be used to losslessly recreate the
original value::