[Python] How to pass tz-aware datetime instances to asyncpg?

When I do everything myself, explicitly, my query works fine:

# start_ts is of PostgreSQL type "timestamp with time zone" aka "timestamptz"
# start & end are datetime.datetime instances with tz=UTC
query += f"WHERE start_ts >= '{ str(start) }'::timestamptz AND start_ts < '{ str(end) }'::timestamptz"
await conn.fetch( query )


When I try to pass them as args and let asyncpg safely interpolate them into the query string on my behalf:

query += "WHERE start_ts >= $1::timestamptz AND start_ts < $2::timestamptz"
await conn.fetch( query, start, end )


I get this error:

CannotCoerceError: cannot cast type text[] to timestamp with time zone


What am I doing wrong?

PS - I wish I could see that actual query that asyncpg is sending PostgreSQL, but I can't find anything in the docs or my google searches on how to enable that.

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