def __init__(self, descriptor_db=None):
self._internal_db = descriptor_database.DescriptorDatabase()<EOL>self._descriptor_db = descriptor_db<EOL>self._descriptors = {}<EOL>self._enum_descriptors = {}<EOL>self._file_descriptors = {}<EOL>
Initializes a Pool of proto buffs.

        The descriptor_db argument to the constructor is provided to allow
        specialized file descriptor proto lookup code to be triggered on demand. An
        example would be an implementation which will read and compile a file
        specified in a call to FindFileByName() and not require the call to Add()
        at all. Results from this database will be cached internally here as well.

        Args:
          descriptor_db: A secondary source of file descriptors.