Subject: From spycopg2 to psycopg3 data adaptation

From: Paolo De Stefani <[email-masked]>
Date: Tue, 05 Oct 2021 13:29:52 +0200

Hi
Still working on migration to psycopg3 of my (not so) small 
application...
I use PyQt\PySide for user interface and i convert some postgresql data 
types to Qt types.
For example to convert timestamptz to QDateTime in psycopg2 i use:

def cast_timestamp_qdatetime(value, cur):
     if value is None:
         return None
     dt = QDateTime.fromString(value[:23], "yyyy-MM-dd HH:mm:ss.zzz")
     if not dt.isValid(): # no milliseconds
         dt = QDateTime.fromString(value[:19], "yyyy-MM-dd HH:mm:ss")
     return dt

QDATETIME = psycopg2.extensions.new_type((1184,), "QDATETIME", 
cast_timestamp_qdatetime)
psycopg2.extensions.register_type(QDATETIME)

I tryed this to achieve the same result in psycopg3:

class TimestamptzQDateTimeLoader(Loader):
     def load(self, value):
         if value is None:
             return None
         print(value)
         dt = QDateTime.fromString(value[:23], "yyyy-MM-dd HH:mm:ss.zzz")
         if not dt.isValid(): # no milliseconds
             dt = QDateTime.fromString(value[:19], "yyyy-MM-dd HH:mm:ss")
         return dt

psycopg.adapters.register_loader('timestamptz', 
TimestamptzQDateTimeLoader)

BUT it's not working because the "value" is binary not string:

<memory at 0x000000000939BA00>

So how i can get the same result of psycopg2 in psycopg3 ?

-- 
Paolo De Stefani

---

From: Daniele Varrazzo <[email-masked]>
Date: Tue, 5 Oct 2021 14:05:12 +0200

> class TimestamptzQDateTimeLoader(Loader):

A `None` will never make it here: you can drop this check in psycopg 3.

> So how i can get the same result of psycopg2 in psycopg3 ?

You can use bytes(value) to get the value as bytes string, and if you
need a str you can use bytes(value).decode()

-- Daniele