[Python-Dev] PEP 410 (Decimal timestamp): the implementation is ready for a review

[Larry Hastings]

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_mtime

The 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