"Kent Johnson" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED]
Martin Häcker wrote:
Hi there,
I just tried to run this code and failed miserably - though I dunno why. Could any of you please enlighten me why this doesn't work?
Here is a simpler test case. I'm mystified too:
from datetime import datetime
class time (datetime): def __init__(self, hours=0, minutes=0, seconds=0, microseconds=0): datetime.__init__(self, 2001, 10, 31, hours, minutes, seconds,
microseconds)
print time(1,2,3,4) # => 0001-02-03 04:00:00 print time() # => TypeError: function takes at least 3 arguments (0
given)
What happens to the default arguments to time.__init__? What happens to
the 2001, 10, 31 arguments
to datetime.__init__?
I would expect the output to be 2001-10-31 01:02:03.000004 2001-10-31 00:00:00.000000
Kent
I can't explain this behavior, but this version does work (uses datetime.combine instead of ctor)
-- Paul
from datetime import datetime, date as dt_date, time as dt_time
class time_d (datetime): def __new__(cls, *args): # default to no microseconds if len(args)==3: args = args + (0,) if len(args)==4: tmpdate = datetime.today() h, mi, s, ms = args return datetime.combine(tmpdate, dt_time(h,mi,s,ms)) elif len(args)==7: y,m,d,h,mi,s,ms = args return datetime.combine(dt_date(y,m,d), dt_time(h,mi,s,ms)) else: raise TypeError, "wrong number of args"
print time_d(2001,10,31,1,2,3,4) print time_d(1,2,3,4) print time_d(1,2,3)
Ah, right. The light turns on...
datetime is immutable so overriding the constructor doesn't change the constructed object. You have to override __new__ instead.
http://www.python.org/2.2.1/descrintro.html#__new__
This works:
from datetime import datetime
class time (datetime):
def __new__(cls, hours=0, minutes=0, seconds=0, microseconds=0):
return datetime.__new__(cls, 2001, 10, 31, hours, minutes, seconds,
microseconds)print time(1,2,3,4) # => 2001-10-31 01:02:03.000004 print time() # => 2001-10-31 00:00:00
Kent
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