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[Python-Dev] PEP 410 (Decimal timestamp): the implementation is ready for a review
Larry Hastingslarry at hastings.org
Thu Feb 16 04:28:01 CET 2012
On 02/15/2012 09:43 AM, Guido van Rossum wrote:> *Apart* from the specific use case of making an exact copy of a> directory tree that can be verified by other tools that simply compare> the nanosecond times for equality,A data point on this specific use case. The following code throws its assert ~90% of the time in Python 3.2.2 on a modern Linux machine (assuming "foo" exists and "bar" does not): import shutil import os shutil.copy2("foo", "bar") assert os.stat("foo").st_mtime == os.stat("bar").st_mtimeThe problem is with os.utime. IIUC stat() on Linux added nanosecond atime/mtime support back in 2.5. But the corresponding utime() functions to write nanosecond atime/mtime didn't appear until relatively recently--and Python 3.2 doesn't use them. With stat_float_times turned on, os.stat effectively reads with ~100-nanosecond precision, but os.utime still only writes with microsecond precision. I fixed this in trunk last September (issue 12904); os.utime now preserves all the precision that Python currently conveys.One way of looking at it: in Python 3.2 it's already pretty bad and almost nobody is complaining. (There's me, I guess, but I scratched my itch.)/arry
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