Classifying time periods in new field using Python Parser of ArcGIS Desktop?

Question

I have a datetime field (Horario) in my feature class, showing only the time. Although the date doesn't appear, it seem to be stored automatically as 30 Dec 1899, I'm not sure why.

I want to use this field to populate another field (Periodo) , where I'll have different periods of the day: morning (6 am - 12pm), afternoon (12pm - 6pm), evening (6pm - 12am) and night (12am - 6am).

I'm trying to write an if-elif statement on the Field Calculator, but I'm always having an "invalid syntax" error, and I'm guessing that's because of the datetime expression I'm using. Can anyone see what's wrong?

def Reclass(horario):
    if (horario < date '1899-12-30 12:00:00' and horario >= date '1899-12-30 06:00:00'):
        return "Manhã (6-12h)"
    elif (horario < date '1899-12-30 18:00:00' and horario >= date '1899-12-30 12:00:00'):
        return "Tarde (12-18h)"
    elif (horario <= date '1899-12-30 23:59:00' and horario >= date '1899-12-30 18:00:00'):
        return "Noite (18-24h)"
    elif (horario < date '1899-12-30 06:00:00' and horario >= date '1899-12-30 00:00:00'):
        return "Madrugada (0-6h)"

Reclass(!Horário!)

I'm thinking the problem is I'm referring to the date as

date '1899-12-30 06:00:00'

How should I refer to datetime fields when using Python?

Answer 1

Using cursors is a good way to inspect how datetime fields can be accessed and written to. This is taken from a feature class, with a a date field:

with arcpy.da.SearchCursor("poly_small", ("COL_DATE")) as cursor:
     for row in cursor:
        print row[0], type(row[0])

---

2014-07-18 06:03:05 <type 'datetime.datetime'>
2014-07-17 00:00:00 <type 'datetime.datetime'>

So, the easiest way to build this would be with the datetime module.

from datetime import datetime as dt    
test = dt(2014, 7, 18, 6, 3, 5)

with arcpy.da.SearchCursor("poly_small", ("COL_DATE")) as cursor:
     for row in cursor:
        print row[0], type(row[0]), row[0] == test

---

2014-07-18 06:03:05 <type 'datetime.datetime'> True
2014-07-17 00:00:00 <type 'datetime.datetime'> False

Instead of using and, there is a simpler way to check if a number lies between two numbers see here I believe the following is correct:

def Reclass(horario):

    if dt(1899,12,30, 12,0,0) > horario  >= dt(1899,12,30, 6,0,0):
        return "Manhã (6-12h)"

    elif dt(1899,12,30, 18,0,0) > horario >= dt(1899,12,30, 12,0,0):
        return "Tarde (12-18h)"

    elif dt(1899,12,30, 23,59,0) >= horario >= dt(1899,12,30, 18,0,0):
        return "Noite (18-24h)"

    elif dt(1899,12,30, 6,0,0) > horario >= dt(1899,12,30, 0,0,0):
        return "Madrugada (0-6h)"