construct

What it is and what it does

Construct is a library for defining binary data formats declaratively. Instead of writing imperative parsing code, you describe your data structure once—specifying fields, their types, sizes, and relationships—and Construct uses that definition in both directions: to parse binary data into Python objects and to build those objects back into binary. The library supports atomic constructs (integers, bytes, strings) and composite ones (structs, sequences, arrays, bitwise fields), plus advanced features like conditional branching, lazy parsing, pointers, and compression tunneling.

It's designed for developers who work with binary protocols, file formats, or network packets and want to avoid hand-rolling parse/build logic. The symmetry means your format definition is the single source of truth, reducing bugs and maintenance burden. Construct supports Python 3.6 through 3.11 and has no runtime dependencies, making it lightweight to add to any project.

Use it for:

• Parse and build custom binary file formats (e.g., image headers, game assets, firmware blobs).
• Define and handle network protocol structures with bit-level field control.
• Reverse-engineer binary data formats by declaratively specifying their layout.
• Build serialization layers for embedded systems or low-level communication.
• Test binary parsers by round-tripping data through parse and build operations.

Worth the install?

AI-flagged interpretation of the facts on this page — verify before relying

Construct is a declarative parser and builder for binary data that lets you define a data structure once and use it symmetrically to both parse binary into Python objects and build objects back into binary.

Yes. Construct is stable, permissive-licensed, dependency-free, and well-suited for any project involving binary data parsing or building. The aging maintenance status (last release 989 days ago) is a minor concern but not a blocker—the API is mature and the repository remains active. Install it if you need declarative binary format handling.

Install

construct on PyPI

pip install construct

uv add construct

poetry add construct

Installing construct

Before you install

Low friction: pure Python wheel with no runtime dependencies. Maintenance is aging—last release was 989 days ago—but the repository remains active with recent commits and the package is marked Production/Stable.

License in practice

MIT license is permissive; you can use this in commercial and proprietary projects with minimal restrictions, provided you include the license notice.

Quickstart

from construct import Struct, Int8ub, Array, Const, Byte, this

format = Struct(
    "signature" / Const(b"BMP"),
    "width" / Int8ub,
    "height" / Int8ub,
    "pixels" / Array(this.width * this.height, Byte),
)
data = format.build(dict(width=3, height=2, pixels=[7,8,9,11,12,13]))
parsed = format.parse(data)

Verify before relying

• Whether the 989-day gap since last release signals maintenance concerns or reflects API stability.
• Performance characteristics for large or deeply nested binary structures.

Package facts

Evidence: construct-2.10.70-py3-none-any.whl

Keywords: construct, kaitai, declarative, data structure, struct, binary, symmetric, parser, builder, parsing, building, pack, unpack, packer, unpacker

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