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Created on 2011-09-02 23:07 by SchorschMCMLX, last changed 2022-04-11 14:57 by admin. This issue is now closed.
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| File name | Uploaded | Description | Edit | |
| python-error.txt | SchorschMCMLX, 2011-09-02 23:07 | IDLE log demonstrating the Python output | ||
| Messages (5) | |||
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| msg143443 - (view) | Author: Dr. Georg Ströhlein (SchorschMCMLX) | Date: 2011-09-02 23:07 | |
Hi all,
I think there is a long-standing bug (it has made it into books on Google...) in the struct.pack() function, at least if the 'd' format string is selected. On both Win and Ubuntu the string returned for pack('!d',1.2345) is '?\xf3\xc0\x83\x12n\x97\x8d', whereas the correct 8 (!!) bytes are 3F F3 C0 83 12 6E 97 8D.
Link to a published VBA UDF for Excel is in the file; that UDF reproduces the examples given in wikipedia on the IEEE 754 / DP pages correctly.
Regards, Schorsch
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| msg143444 - (view) | Author: Dr. Georg Ströhlein (SchorschMCMLX) | Date: 2011-09-02 23:15 | |
link is here: http://carolomeetsbarolo.files.wordpress.com/2011/08/double_2_hex.pdf |
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| msg143454 - (view) | Author: Mark Dickinson (mark.dickinson) *  |
Date: 2011-09-03 07:22 | |
I agree with you on the correct 8 output bytes. And those expected bytes are exactly what struct.pack is producing here:
Python 2.7.2 |EPD 7.1-1 (32-bit)| (default, Jul 3 2011, 15:40:35)
[GCC 4.0.1 (Apple Inc. build 5493)] on darwin
Type "packages", "demo" or "enthought" for more information.
>>> import struct
>>> struct.pack('!d', 1.2345)
'?\xf3\xc0\x83\x12n\x97\x8d'
>>> len(struct.pack('!d', 1.2345))
8
>>> struct.pack('!d', 1.2345).encode('hex')
'3ff3c083126e978d'
I suspect that the confusion arises from the way the output string is displayed: the 8 bytes in the output string are escaped if they're not printable ASCII characters, and are displayed directly otherwise (notice the '?' and the 'n', with codes 0x3f and 0x63 respectively).
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| msg143456 - (view) | Author: Mark Dickinson (mark.dickinson) * |
Date: 2011-09-03 07:26 | |
> with codes 0x3f and 0x63 respectively Whoops: that should be '... 0x3f and 0x6e ...'. |
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| msg143458 - (view) | Author: Dr. Georg Ströhlein (SchorschMCMLX) | Date: 2011-09-03 09:18 | |
Thank you, Mark, for explaining the details of how to "correctly" format the output of that command to me... Regards, Schorsch |
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| History | |||
|---|---|---|---|
| Date | User | Action | Args |
| 2022-04-11 14:57:21 | admin | set | github: 57098 |
| 2011-09-03 09:18:26 | SchorschMCMLX | set | messages: + msg143458 |
| 2011-09-03 07:26:16 | mark.dickinson | set | messages: + msg143456 |
| 2011-09-03 07:22:45 | mark.dickinson | set | status: open -> closed nosy: + mark.dickinson messages: + msg143454 resolution: not a bug |
| 2011-09-02 23:15:20 | SchorschMCMLX | set | messages: + msg143444 |
| 2011-09-02 23:07:32 | SchorschMCMLX | create | |