How to programmatically fill a datetime field with datetime.datetime.now() function

Question

I have been trying to programmatically fill a datetime field using values coming from datetime.datetime.now() function.

#I create the temp shp using a URI
URI = 'MultiPolygon?crs=epsg:3857&field=id:integer&field=x:integer&field=y:integer&field=z:integer&field=bx:integer&field=by:integer&field=bz:integer&field=rating:integer&field=timestamp:datetime&index=yes'
# temp shp
mem_layer = QgsVectorLayer(URI, 'temp', 'memory')

# when I try to fill out the timestamp field with a variable now
now = datetime.datetime.now()
# I get an empty or zero value field

It looks like I have to cast the variable first to a string to make it work but in that case I lose the capability to make calculation over the field (I do need to keep track of time to evaluate the "duration" of a specific action triggered by the user)

I tried with the following datatypes with no luck:

date

datetime

real

double

Which datatype should I use when creating the shp in order for it to be filled with that specific value?

Answer 1

A Shapefile stores dates in a date field with this format: yyyy-mm-dd. So some string formatting is required.

import datetime

now = datetime.datetime.now()
month = now.month
year = now.year
day = now.day

formatted = "%s-%s-%s" % (year, month, day) 

or

from datetime import datetime

now = datetime.now()
formatted = now.strftime('%Y-%m-%d')

Answer 2

Sounds like to me you need the full datetime not just the date. If that is the case, then I would recommend you store it as a string, then convert it back to a datetime to do your calculation.

Alternatively, you could parse the datetime object and store all the components in a separate field. So you could store the date in the date field, then store the time as a double using 24hr base.