[issue14896] plistlib handling of real datatype
Ned Deily
report at bugs.python.org
Thu May 24 05:17:01 CEST 2012
Ned Deily <nad at acm.org> added the comment:
This should no longer be an issue on most platforms as of Python 2.7 and Python 3.1. Both added a new algorithm such that "the repr() of a floating-point number x now returns a result based on the shortest decimal string that’s guaranteed to round back to x under correct rounding". The new float repr applies to plistlib as well. Here's an example:
$ cat pl.py
from plistlib import readPlistFromString, writePlistToString
d1 = dict(a=0.15)
s1 = writePlistToString(d1)
print(s1)
d2 = readPlistFromString(s1)
print(d2)
assert d1['a'] == d2['a']
print(d2['a'].hex())
$ python2.6 pl.py
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>a</key>
<real>0.14999999999999999</real>
</dict>
</plist>
{'a': 0.14999999999999999}
0x1.3333333333333p-3
$ python2.7 pl.py
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>a</key>
<real>0.15</real>
</dict>
</plist>
{'a': 0.15}
0x1.3333333333333p-3
Note that the binary representation of the float is the same on both 2.6 and 2.7 in this case anyway.
For more info, see:
http://docs.python.org/py3k/whatsnew/3.1.html#other-language-changes
http://docs.python.org/whatsnew/2.7.html#other-language-changes
----------
nosy: +ned.deily
resolution: -> out of date
stage: -> committed/rejected
status: open -> closed
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<http://bugs.python.org/issue14896>
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