¿Cómo guardar un archivo de imagen en una base de datos de Postgres?

Normalmente no escribo programas de ejemplo completos para personas, pero no lo exigiste y es bastante simple, así que aquí tienes:

#!/usr/bin/env python3

import os
import sys
import psycopg2
import argparse

db_conn_str = "dbname=regress user=craig"

create_table_stm = """
CREATE TABLE files (
    id serial primary key,
    orig_filename text not null,
    file_data bytea not null
)
"""

def main(argv):
    parser = argparse.ArgumentParser()
    parser_action = parser.add_mutually_exclusive_group(required=True)
    parser_action.add_argument("--store", action='store_const', const=True, help="Load an image from the named file and save it in the DB")
    parser_action.add_argument("--fetch", type=int, help="Fetch an image from the DB and store it in the named file, overwriting it if it exists. Takes the database file identifier as an argument.", metavar='42')
    parser.add_argument("filename", help="Name of file to write to / fetch from")

    args = parser.parse_args(argv[1:])

    conn = psycopg2.connect(db_conn_str)
    curs = conn.cursor()

    # Ensure DB structure is present
    curs.execute("SELECT 1 FROM information_schema.tables WHERE table_schema = %s AND table_name = %s", ('public','files'))
    result = curs.fetchall()
    if len(result) == 0:
        curs.execute(create_table_stm)

    # and run the command
    if args.store:
        # Reads the whole file into memory. If you want to avoid that,
        # use large object storage instead of bytea; see the psycopg2
        # and postgresql documentation.
        f = open(args.filename,'rb')

        # The following code works as-is in Python 3.
        #
        # In Python 2, you can't just pass a 'str' directly, as psycopg2
        # will think it's an encoded text string, not raw bytes. You must
        # either use psycopg2.Binary to wrap it, or load the data into a
        # "bytearray" object.
        #
        # so either:
        #
        #   filedata = psycopg2.Binary( f.read() )
        #
        # or
        #
        #   filedata = buffer( f.read() )
        #
        filedata = f.read()
        curs.execute("INSERT INTO files(id, orig_filename, file_data) VALUES (DEFAULT,%s,%s) RETURNING id", (args.filename, filedata))
        returned_id = curs.fetchone()[0]
        f.close()
        conn.commit()
        print("Stored {0} into DB record {1}".format(args.filename, returned_id))

    elif args.fetch is not None:
        # Fetches the file from the DB into memory then writes it out.
        # Same as for store, to avoid that use a large object.
        f = open(args.filename,'wb')
        curs.execute("SELECT file_data, orig_filename FROM files WHERE id = %s", (int(args.fetch),))
        (file_data, orig_filename) = curs.fetchone()

            # In Python 3 this code works as-is.
            # In Python 2, you must get the str from the returned buffer object.
        f.write(file_data)
        f.close()
        print("Fetched {0} into file {1}; original filename was {2}".format(args.fetch, args.filename, orig_filename))

    conn.close()

if __name__ == '__main__':
    main(sys.argv)

Escrito con Python 3.3. El uso de Python 2.7 requiere que lea el archivo y lo convierta a un buffer objeto o utilizar las funciones de objetos grandes. La conversión a Python 2.6 y anteriores requiere la instalación de argparse, probablemente otros cambios.

Querrá cambiar la cadena de conexión de la base de datos a algo adecuado para su sistema si va a probarlo.

Si está trabajando con imágenes grandes, considere usar psycopg2's compatibilidad con objetos grandes en lugar de bytea - en particular, lo_import para tienda, lo_export para escribir directamente en un archivo, y las funciones de lectura de objetos grandes para leer pequeños fragmentos de la imagen a la vez.