inserting/retriving dates in psycopg

[Michele Simionato]

Look at this example:
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

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

 

[Frank Millman]

Look at this example:
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

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

 

[Michele Simionato]

Frank Millman:

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

This is exactly the type checking I would like to avoid :-/

Michele Simionato

 

[Frank Millman]

Frank Millman:



This is exactly the type checking I would like to avoid :-/

Michele Simionato

psycopg returns a datetime.datetime object from a TIMESTAMP column, and
a datetime.date object from a DATE column. You should not have to do
any type checking unless you are doing something odd, like I am, and
wanting to convert them all into datetime.datetime objects.

Perhaps if you explain what you are trying to do, I may be able to
suggest something.

Frank

 

[Michele Simionato]

Frank Millan:

Perhaps if you explain what you are trying to do, I may be able to
suggest something.

I am looking for an adaptation/type cast mechanism and looking at the
sources I think I have
found it in doc/examples/usercast.py. I am doing some experiment now
....

Michele Simionato