strftime function from django.utils.datetime_safe doesn't work properly in years below 1000

[Javier de la Rosa]

If a model has a DateTimeField attribute, in order to serialize the objects, django uses the format "%Y/%m/%d". However the function strftime doesn't handle properly the option "%Y" in years below 1000: instead to fill with zeros (0) until to complete the 4 digits, it uses spaces. Therefore, at deserialization time django raises a exception.

Currently

>>> datetime_safe.date(850, 8, 2).strftime("%Y/%m/%d")
' 850/00/02'

It must to be

>>> datetime_safe.date(850, 8, 2).strftime("%Y/%m/%d")
'0850/00/02'

The simplest patch is atached, but this issue can be deeper.

[Javier de la Rosa]

strftime filling with zeros in years below 1000

[Ramiro Morales]

Duplicate of #10866.