You can't use stftime.
You have to manually build a string with the format you want using the
other methods inside DateTime.

e.g. fetcha.aCommonZ() or build up your date using
components such as; fetcha.day()  fetcha.month()  fetcha.year()



I made a script what recive a parameter fecha(f)
script pFecha:
s="%02d-%02d-%04d"
s=s % (f.day(),f.month(),f.year())
print s
return printed


the call is <td tal:content="python: container/pFecha(item.fecha)">

Thanks