Parse dates from before the year 1000

Question

Consider the following example:

from datetime import datetime


FMT = "%Y-%m-%dT%H:%M:%S"

original_date = datetime(1,1,1)

s = original_date.strftime(FMT)  # This is '1-01-01T00:00:00'

When I now try to parse that string back into a datetime with the exact format I used to serialize it in the first place, a ValueError is thrown at me:

datetime.strptime(s, FMT)

ValueError: time data '1-01-01T00:00:00' does not match format '%Y-%m-%dT%H:%M:%S'

However

datetime.strptime('0001-01-01T00:00:00', FMT)

works as expected. I would have expected strptime to be able to handle whatever strftime produces. I always regarded those functions to be the inverse of each other.

Why does original_date.strftime(FMT) not result in a zero-padded year? Is there any reason for this inconsistency?

Answer 1

The results for %Y are not consistent across platforms. On Mac OS X it'll return 0001 but on Linux it returns 1.

On Linux you can use %4Y to produce 0001 as year value.

This is a known issue: https://bugs.python.org/issue13305.

The documentation for strftime() and strptime() also states:

The full set of format codes supported varies across platforms, because Python calls the platform C library’s strftime() function, and platform variations are common. To see the full set of format codes supported on your platform, consult the strftime(3) documentation.