3. Advanced Concepts#

Now that you’ve gained a basic understanding of how the library works, we can dive deeper into more advanced concepts. This section will help you master the usage of specialized features, and by the end of this tutorial, you’ll be well-equipped to create and manipulate your own custom struct classes in Python.

Attention

Please note that many of the structs and techniques presented here are still evolving. For instance, the BitField class is still being refined, and its current usage may not be as intuitive as you might expect.

Advanced Topics for Catepillar (Python)

The End!

We finish this tutorial by completing our PNG format implementation. As the format is just a collection of chunks, we can simply alter the main struct from before:

Final PNG implementation#
@struct
class PNG:
    magic: b"\x89PNG\x0D\x0A\x1A\x0A"
    # We don't know the length, therefore we need greedy parsing
    chunks: PNGChunk[...]

Thats it! We now have a qualified PNG image parser and builder just using some Python class definitions.

Sample usage of the PNG struct#
>>> image = unpack_file(PNG, "/path/to/image.png")
>>> image
PNG(magic=b'\x89PNG\r\n\x1a\n', chunks=[PNGChunk(length=13,type='IHDR', body=..., crc=258163462), ...])
>>> pack_file(image, "/path/to/destination")

This is the end of our journy to the basics of caterpillar. Below is a collection of useful resources that might help you progress any further.

See also

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