A simple and safe SQLite3 backup script written in Python using ctypes + sqlite3 online backup API

sqlite_backup.py

#! /usr/bin/env python
# Of course, the author does not guarantee safety.
# I did my best by using SQLite's online backup API.
from __future__ import print_function
import sys, ctypes
from ctypes.util import find_library

SQLITE_OK = 0
SQLITE_ERROR = 1
SQLITE_BUSY = 5
SQLITE_LOCKED = 6

SQLITE_OPEN_READONLY = 1
SQLITE_OPEN_READWRITE = 2
SQLITE_OPEN_CREATE = 4

sqlite = ctypes.CDLL(find_library('sqlite3'))
sqlite.sqlite3_backup_init.restype = ctypes.c_void_p

if __name__ == '__main__':
    p_src_db = ctypes.c_void_p(None)
    p_dst_db = ctypes.c_void_p(None)
    null_ptr = ctypes.c_void_p(None)

    ret = sqlite.sqlite3_open_v2(sys.argv[1], ctypes.byref(p_src_db), SQLITE_OPEN_READONLY, null_ptr)
    assert ret == SQLITE_OK
    assert p_src_db.value is not None
    ret = sqlite.sqlite3_open_v2(sys.argv[2], ctypes.byref(p_dst_db), SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, null_ptr)
    assert ret == SQLITE_OK
    assert p_dst_db.value is not None

    print('starting backup...')
    p_backup = sqlite.sqlite3_backup_init(p_dst_db, 'main', p_src_db, 'main')
    print('  backup handler: {0:#08x}'.format(p_backup))
    assert p_backup is not None

    while True:
        ret = sqlite.sqlite3_backup_step(p_backup, 20)
        remaining = sqlite.sqlite3_backup_remaining(p_backup)
        pagecount = sqlite.sqlite3_backup_pagecount(p_backup)
        print('  backup in progress: {0:.2f}%'.format((pagecount - remaining) / float(pagecount) * 100))
        if remaining == 0:
            break
        if ret in (SQLITE_OK, SQLITE_BUSY, SQLITE_LOCKED):
            sqlite.sqlite3_sleep(100)

    sqlite.sqlite3_backup_finish(p_backup)

    sqlite.sqlite3_close(p_dst_db)
    sqlite.sqlite3_close(p_src_db)

In python3 i had to convert all unicode strings to bytes bytes(sys.argv[1], 'ascii'), , bytes(sys.argv[2], 'ascii'), and

p_backup = sqlite.sqlite3_backup_init(p_dst_db, bytes('main', 'ascii'),
                                      p_src_db, bytes('main', 'ascii'))