如何在游标上覆盖psycopg2 tzinfo_factory

Question

So because of [reasons], I'm looking at overriding the tzinfo classes that are set by pyscopg2. I thought this would be a simple case of overriding tzinfo_factory on the cursor class. However, this doesn't seem to work.

import psycopg2
from psycopg2.extensions import cursor
from psycopg2.tz import FixedOffsetTimezone

class MyFixedOffsetTimezone(FixedOffsetTimezone):
    pass

class MyCursorFactory(cursor):
    tzinfo_factory = MyFixedOffsetTimezone
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

conn = psycopg2.connect('', cursor_factory=MyCursorFactory)
cursor = conn.cursor()
cursor.execute("select now()")
results = cursor.fetchall()
print(results[0][0].tzinfo)
print(results[0][0].tzinfo.__class__)

Will still give you

$ python3 example.py 
psycopg2.tz.FixedOffsetTimezone(offset=60, name=None)
<class 'psycopg2.tz.FixedOffsetTimezone'>

Is this a result of my fundamental misunderstanding of how the C implementation's members and the higher level python interact? (or am I being a complete pleb?) versions: python 3.5.2 tested in psycopg2 2.6.2 and 2.7.1

I've trawled through the code, and it does seem to be referencing tzinfo_factory on the cursor (psycopg/typecast_datetime.c:typecast_PYDATETIME_cast line 140 @ 2.7.1)

tzinfo_factory = ((cursorObject *)curs)->tzinfo_factory;

Answer 1

You have to pass the cursor_factory=... and assign MyFixedOffsetTimezone to MyCursorFactory:

class MyFixedOffsetTimezone(FixedOffsetTimezone):
    pass

class MyCursorFactory(cursor):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.tzinfo_factory = MyFixedOffsetTimezone

conn = psycopg2.connect('...')
cursor = conn.cursor(cursor_factory=MyCursorFactory)
cursor.execute("select now()")
results = cursor.fetchall()
print(results[0][0].tzinfo)
print(results[0][0].tzinfo.__class__)

returns:

psycopg2.tz.FixedOffsetTimezone(offset=120, name=None)
<class '__main__.MyFixedOffsetTimezone'>