inserting/retriving dates in psycopg

Frank Millman frank at chagford.com
Thu Jan 5 08:55:38 CET 2006


Michele Simionato wrote:
> Look at this example:
>
> >>> import psycopg
> >>> psycopg.__version__
> '1.1.19'
> >>> import datetime
> >>> today = datetime.datetime.today()
> >>> co = psycopg.connect('')
> >>> cu = co.cursor()
>
> >>> cu.execute('CREATE TABLE example (date date)')
> >>> cu.execute("INSERT into example VALUES (%s)", (today,))
> Traceback (most recent call last):
>   File "/usr/lib/python2.4/doctest.py", line 1243, in __run
>     compileflags, 1) in test.globs
>   File "<doctest __main__[6]>", line 1, in ?
>     cu.execute("INSERT into example VALUES (%s)", (today,))
> ProgrammingError: ERROR:  syntax error at or near "17" at character 40
>
>     INSERT into example VALUES (2006-01-04 17:19:03.354615)
>
> Is there a smart way of solving this, without stripping the date by
> hand?
> Also, if I insert the date as a string
>
> >>> cu.execute("INSERT into example VALUES ('2006-01-04')")
> >>> co.commit()
>
> I get back a DateTime object (I think a mxDateTime object)
>
> >>> cu.execute("SELECT * from example")
> >>> d = cu.fetchone()[0]
> >>> print type(d)
>  <type 'DateTime'>
>
> and NOT a datetime.datetime.
>
> So I need an adaptation mechanism; alternatively it would be enough for
> me to be able
> to redefine the __str__ representation of psycopg DateTime objects (
> which are defined
> at C level, so I cannot just override the __str__ method).
>
> Any  hints? I am sure there is a custom way to do this.
>
>                 Michele Simionato

I am no expert, but as I have not seen any other replies, I will
explain how I do it.

Firstly, I seem to recall that when you install psycopg, it tries to
guess whether to compile it for mx.DateTime or the built-in datetime
module, based on version of Python, whether mx is installed, etc. I am
sure it is possible to force it to choose your preferred one by
modifying the .cfg file (I think).

Assuming it is set up correctly for the datetime module, this is how I
insert and retrieve.

If I have a datetime.datetime instance called dat, I insert it using
str(dat).

I found retrieving a bit trickier, as I have standardised on using the
datetime.datetime type throughout my app, but I have a mixture of DATE
and TIMESTAMP types in my database. Therefore I convert the result as
follows -

import datetime as dt

def DbToDate(dat):
    if isinstance(dat,dt.datetime):
        return dat  # already in datetime format
    if isinstance(dat,dt.date):
        return dt.datetime.combine(dat,dt.time(0))  # convert to
datetime

HTH

Frank Millman




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