fdbbc3a20d
This does introduce some not-so-nice things, like having to annotate each `__init__` function with `-> None`. However, the benefits of having static type checking in a complex bit of software like BAT outweigh the downsides.
58 lines
1.8 KiB
Python
58 lines
1.8 KiB
Python
import logging
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import os
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import pathlib
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import struct
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import typing
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from . import dna_io, exceptions
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log = logging.getLogger(__name__)
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class BlendFileHeader:
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"""
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BlendFileHeader represents the first 12 bytes of a blend file.
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It contains information about the hardware architecture, which is relevant
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to the structure of the rest of the file.
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"""
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structure = struct.Struct(b'7s1s1s3s')
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def __init__(self, fileobj: typing.IO[bytes], path: pathlib.Path) -> None:
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log.debug("reading blend-file-header %s", path)
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fileobj.seek(0, os.SEEK_SET)
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header = fileobj.read(self.structure.size)
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values = self.structure.unpack(header)
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self.magic = values[0]
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pointer_size_id = values[1]
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if pointer_size_id == b'-':
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self.pointer_size = 8
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elif pointer_size_id == b'_':
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self.pointer_size = 4
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else:
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raise exceptions.BlendFileError('invalid pointer size %r' % pointer_size_id, path)
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endian_id = values[2]
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if endian_id == b'v':
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self.endian = dna_io.LittleEndianTypes
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self.endian_str = b'<' # indication for struct.Struct()
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elif endian_id == b'V':
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self.endian = dna_io.BigEndianTypes
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self.endian_str = b'>' # indication for struct.Struct()
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else:
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raise exceptions.BlendFileError('invalid endian indicator %r' % endian_id, path)
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version_id = values[3]
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self.version = int(version_id)
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def create_block_header_struct(self) -> struct.Struct:
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"""Create a Struct instance for parsing data block headers."""
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return struct.Struct(b''.join((
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self.endian_str,
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b'4sI',
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b'I' if self.pointer_size == 4 else b'Q',
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b'II',
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)))
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