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Kirill Smelkov
cpython
Commits
fee346b5
Commit
fee346b5
authored
Apr 17, 2009
by
Raymond Hettinger
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Doc/whatsnew/3.1.rst
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fee346b5
...
...
@@ -155,7 +155,7 @@ Some smaller changes made to the core Python language are:
The significance is easily seen with a number like ``1.1`` which does not
have an exact equivalent in binary floating point. Since there is no exact
equivalent, an expression like ``float(
"1.1"
)`` evaluates to the nearest
equivalent, an expression like ``float(
'1.1'
)`` evaluates to the nearest
representable value which is ``0x1.199999999999ap+0`` in hex or
``1.100000000000000088817841970012523233890533447265625`` in decimal. That
nearest value was and still is used in subsequent floating point
...
...
@@ -163,16 +163,16 @@ Some smaller changes made to the core Python language are:
What is new is how the number gets displayed. Formerly, Python used a
simple approach. The value of ``repr(1.1)`` was computed as ``format(1.1,
'.17g')`` which evaluate
s
to ``'1.1000000000000001'``. The advantage of
'.17g')`` which evaluate
d
to ``'1.1000000000000001'``. The advantage of
using 17 digits was that it relied on IEEE-754 guarantees to assure that
``eval(repr(1.1))`` would round-trip exactly to its original value. The
disadvantage is that many people found the output to be confusing (mistaking
intrinsic limitations of binary floating point representation as being a
problem with Python itself).
The new algorithm for ``repr(1.1)`` is smarter and returns ``
1.1
``.
The new algorithm for ``repr(1.1)`` is smarter and returns ``
'1.1'
``.
Effectively, it searches all equivalent string representations (ones that
get stored
as
the same underlying float value) and returns the shortest
get stored
with
the same underlying float value) and returns the shortest
representation.
The new algorithm tends to emit cleaner representations when possible, but
...
...
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