binary_file_parser.py

# Copyright 2017 Google Inc.
# 
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# 
# https://www.apache.org/licenses/LICENSE-2.0
# 
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import struct
from struct import unpack


def unpack_drawing(file_handle):
    key_id, = unpack('Q', file_handle.read(8))
    countrycode, = unpack('2s', file_handle.read(2))
    recognized, = unpack('b', file_handle.read(1))
    timestamp, = unpack('I', file_handle.read(4))
    n_strokes, = unpack('H', file_handle.read(2))
    image = []
    for i in range(n_strokes):
        n_points, = unpack('H', file_handle.read(2))
        fmt = str(n_points) + 'B'
        x = unpack(fmt, file_handle.read(n_points))
        y = unpack(fmt, file_handle.read(n_points))
        image.append((x, y))

    return {
        'key_id': key_id,
        'countrycode': countrycode,
        'recognized': recognized,
        'timestamp': timestamp,
        'image': image
    }


def unpack_drawings(filename):
    with open(filename, 'rb') as f:
        while True:
            try:
                yield unpack_drawing(f)
            except struct.error:
                break


for drawing in unpack_drawings('nose.bin'):
    # do something with the drawing
    print(drawing['countrycode'])