CityBufReader.py

import struct

from CityBuf_ import \
  Header, \
  CityFeature

class CityBufReader:
  MAGIC_NUMBER_SIZE = 8

  def __init__(self, file):
    self.f = file
    self.f.seek(0)
    self.read_magic_number()
    self.pos_header = self.MAGIC_NUMBER_SIZE
    self.read_header()
    self.pos_data = self.f.tell()
  
  def read_magic_number(self):
    self.f.seek(0)
    magic_number = self.f.read(self.MAGIC_NUMBER_SIZE)

    if magic_number[:3] == b'FCB' and magic_number[4:7] == b'FCB':
      self.version_major = magic_number[3]
      self.version_minor = magic_number[7]
    else:
      raise Exception('Invalid magic number')

  def read_header(self):
    self.f.seek(self.pos_header)
    self.size_header = struct.unpack('<I', self.f.read(4))[0]

    header_buf = self.f.read(self.size_header)

    # Get a pointer to the root object inside the FlatBuffer
    self.header = Header.Header.GetRootAsHeader(header_buf, 0)

  # iterator over the features
  def features(self):
    self.f.seek(self.pos_data)
    for i in range(self.header.FeaturesCount()):
      feature_length = struct.unpack('<I', self.f.read(4))[0]

      feature_buf = self.f.read(feature_length)
      feature = CityFeature.CityFeature.GetRootAsCityFeature(feature_buf, 0)
      yield feature