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author | Georg Brandl <georg@python.org> | 2009-08-13 08:47:18 (GMT) |
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committer | Georg Brandl <georg@python.org> | 2009-08-13 08:47:18 (GMT) |
commit | 7d1e88063c6241d4750326fc772d5b8a6819a77f (patch) | |
tree | 2aece70a7b09bdcbd64d792029c042d3951c534d /Doc/tutorial | |
parent | 98e472d7fb88e8cf7c7797a879eb63cf3242ed97 (diff) | |
download | cpython-7d1e88063c6241d4750326fc772d5b8a6819a77f.zip cpython-7d1e88063c6241d4750326fc772d5b8a6819a77f.tar.gz cpython-7d1e88063c6241d4750326fc772d5b8a6819a77f.tar.bz2 |
Merged revisions 73656,73658,73663,73666 via svnmerge from
svn+ssh://svn.python.org/python/branches/py3k
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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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Diffstat (limited to 'Doc/tutorial')
-rw-r--r-- | Doc/tutorial/floatingpoint.rst | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/Doc/tutorial/floatingpoint.rst b/Doc/tutorial/floatingpoint.rst index e877a99..0230183 100644 --- a/Doc/tutorial/floatingpoint.rst +++ b/Doc/tutorial/floatingpoint.rst @@ -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:: |