array and struct 64-bit Linux change in behavior Python 3.7 and 2.7
Peter J. Holzer
hjp-python at hjp.at
Sat Dec 7 06:26:37 EST 2019
On 2019-12-02 09:55:16 -0800, Rob Gaddi wrote:
> The struct situation is, as you said, a bit different. I believe that with
> the default native alignment @, you're seeing 4-byte data padded to an
> 8-byte alignment, not 8-byte data.
Nope. That's really an 8 byte long:
Python 3.7.3 (default, Apr 3 2019, 05:39:12)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import struct
>>> struct.pack('L', 0x0807060504030201)
b'\x01\x02\x03\x04\x05\x06\x07\x08'
All 8 bytes are serialized. Trying to serialize 9 bytes (actually only 68
non-zero bits) fails:
>>> struct.pack('L', 0x090807060504030201)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
struct.error: argument out of range
And when you use the "standard size", 8 bytes are also too much:
>>> struct.pack('=L', 0x0807060504030201)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
struct.error: 'L' format requires 0 <= number <= 4294967295
But 4 bytes are ok:
>>> struct.pack('=L', 0x04030201)
b'\x01\x02\x03\x04'
hp
--
_ | Peter J. Holzer | Story must make more sense than reality.
|_|_) | |
| | | hjp at hjp.at | -- Charles Stross, "Creative writing
__/ | http://www.hjp.at/ | challenge!"
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