More puzzling behavior while subclassing datetime

[insyte]

With assistance from Gabriel and Frederik (and a few old threads in
c.l.p.) I've been making headway on my specialized datetime class. Now
I'm puzzled by behavior I didn't expect while attempting to use some of
the alternate datetime constructors. Specifically, it appears if I
call GeneralizedTime .now() it calls the __new__ method of my class but
treats keyword arguments as if they were positional.

My class:

class GeneralizedTime (datetime):
def __new__(cls, time=None, *args, **kwargs):
print time, args, kwargs
if isinstance(time , str):
timeValues, tzOffset = cls.stringToTim eTuple(time)
return datetime.__new_ _(cls, tzinfo=GenericT Z(tzOffset),
**timeValues)
elif isinstance(time , datetime):
timeValues = time.timetuple( )[:6]
tzOffset = time.utcoffset( )
return datetime.__new_ _(cls, tzinfo=GenericT Z(tzOffset),
*timeValues)
elif time is None:
print "Still gotta figure out now to do this one..."
else:
raise Invalidtime(tim e)
@staticmethod
def stringToTimeTup le(timeString):
... regex that parses timeString ...

>>GeneralizedTi me.today()

2006 (11, 16, 0, 35, 18, 747275, None) {}
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "gentime.py ", line 106, in __new__
raise InvalidTime(tim e)
gentime.Invalid Time: 2006

So it appears the time tuple is being passed to
GeneralizedTime .__new__, but the first value is being assigned to the
"time" argument.

Is this a side effect of how datetime is implemented? Or am I doing
something screwy?

Thanks!

-Ben

[wittempj]

in****@gmail.co m wrote:

With assistance from Gabriel and Frederik (and a few old threads in
c.l.p.) I've been making headway on my specialized datetime class. Now
I'm puzzled by behavior I didn't expect while attempting to use some of
the alternate datetime constructors. Specifically, it appears if I
call GeneralizedTime .now() it calls the __new__ method of my class but
treats keyword arguments as if they were positional.

My class:

class GeneralizedTime (datetime):
def __new__(cls, time=None, *args, **kwargs):

datetime.dateti me() takes these arguments: year, month, day[, hour[,
minute[, second[, microsecond[, tzinfo]]]]]), see
http://docs.python.org/lib/datetime-datetime.html

print time, args, kwargs
if isinstance(time , str):
timeValues, tzOffset = cls.stringToTim eTuple(time)
return datetime.__new_ _(cls, tzinfo=GenericT Z(tzOffset),
**timeValues)
elif isinstance(time , datetime):
timeValues = time.timetuple( )[:6]

time.timetuple( ) does not exist, see
http://docs.python.org/lib/module-time.html, time is represented as a
tuple. checkout time.mktime() on how to convert to a tuple to a time

tzOffset = time.utcoffset( )
return datetime.__new_ _(cls, tzinfo=GenericT Z(tzOffset),
*timeValues)
elif time is None:
print "Still gotta figure out now to do this one..."
else:
raise Invalidtime(tim e)
@staticmethod
def stringToTimeTup le(timeString):
... regex that parses timeString ...

>GeneralizedTim e.today()

2006 (11, 16, 0, 35, 18, 747275, None) {}
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "gentime.py ", line 106, in __new__
raise InvalidTime(tim e)
gentime.Invalid Time: 2006

So it appears the time tuple is being passed to
GeneralizedTime .__new__, but the first value is being assigned to the
"time" argument.

Is this a side effect of how datetime is implemented? Or am I doing
something screwy?

Thanks!

-Ben

A very cutback part of your code gets the basics working:
from datetime import datetime
class Invalidtime(Exc eption):
pass

class GeneralizedTime (datetime):
def __new__(cls, *args, **kwargs):
if isinstance(args , tuple):
return datetime.__new_ _(cls, *args)
else:
raise Invalidtime(arg s)

t = GeneralizedTime .today()
print t.year
print t.month
print t.day
print t.hour
print t.minute
print t.second
print t.microsecond
print t.tzinfo

[Peter Otten]

in****@gmail.co m wrote:

With assistance from Gabriel and Frederik (and a few old threads in
c.l.p.) I've been making headway on my specialized datetime class. Now
I'm puzzled by behavior I didn't expect while attempting to use some of
the alternate datetime constructors. Specifically, it appears if I
call GeneralizedTime .now() it calls the __new__ method of my class but
treats keyword arguments as if they were positional.

My class:

class GeneralizedTime (datetime):
def __new__(cls, time=None, *args, **kwargs):
print time, args, kwargs
if isinstance(time , str):
timeValues, tzOffset = cls.stringToTim eTuple(time)
return datetime.__new_ _(cls, tzinfo=GenericT Z(tzOffset),
**timeValues)
elif isinstance(time , datetime):
timeValues = time.timetuple( )[:6]
tzOffset = time.utcoffset( )
return datetime.__new_ _(cls, tzinfo=GenericT Z(tzOffset),
*timeValues)
elif time is None:
print "Still gotta figure out now to do this one..."
else:
raise Invalidtime(tim e)
@staticmethod
def stringToTimeTup le(timeString):
... regex that parses timeString ...

>>>GeneralizedT ime.today()

2006 (11, 16, 0, 35, 18, 747275, None) {}
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "gentime.py ", line 106, in __new__
raise InvalidTime(tim e)
gentime.Invalid Time: 2006

So it appears the time tuple is being passed to
GeneralizedTime .__new__, but the first value is being assigned to the
"time" argument.

Is this a side effect of how datetime is implemented?

Yes. Consider:

>>def today(time=None , *args):

.... print "time = ", time, "args = ", args
....

>>today(2006, 11, 16)

time = 2006 args = (11, 16)

To fix the issue you'll probably have to remove the time=None parameter from
GeneralizedTime .__new__() and instead extract it from args or kwargs.

Peter

[insyte]

Yes. Consider:

>

>def today(time=None , *args):

... print "time = ", time, "args = ", args
...

>today(2006, 11, 16)

time = 2006 args = (11, 16)

To fix the issue you'll probably have to remove the time=None parameter from
GeneralizedTime .__new__() and instead extract it from args or kwargs.

D'oh. That *should* have been obvious.

I am now no longer allowed to program after midnight.

Thanks!

-Ben