construct is a powerful declarative symmetric parser/builder for binary data, supporting Python 3.6+. It allows you to define the structure of binary data using Python objects and then parse or build data according to that structure. The current version is 2.10.70, and it maintains a fairly active release cadence, often releasing minor fixes and improvements.
pip install constructVerified import paths — ran on the pinned version, not inferred.
This quickstart demonstrates how to define a `Struct` using various constructors like `Bytes`, `Int8ub`, `Array`, and `GreedyRange`. It shows how to use lambda functions within a structure definition to refer to previously parsed fields (e.g., `ctx.count`). Finally, it illustrates building Python objects into binary data and parsing binary data back into Python objects, including basic error handling.
Migrate your code to the modern construct API (2.8+ is recommended). This will likely involve a complete rewrite of your structure definitions and parsing/building logic. Refer to the official construct documentation for the current API.
Review the changelog for versions 2.8 and 2.9. Update `Subconstruct` usage to directly use the base construct, rename `RepeatUntil` to `GreedyRange`, and adjust conditional error handling if `Context.error_when` was used.
If you need to reuse a construct with different parameters or ensure isolation, create a new instance each time, or use `construct.deep_copy` if you're modifying a complex, nested structure and need a true independent copy.
Thoroughly understand the `Context` object and how `this` (or `ctx`) dynamically refers to the current parsing/building context. Debug with `construct.Probe` to inspect the context at various points in your structure definition. Ensure fields are defined before they are referenced via `this`.
Install the library using pip: `pip install construct`.
Ensure the input binary data provided to the `parse()` method is complete and matches the structure defined by the construct. You might need to check the source of your binary data or adjust the construct's definition if the data length is variable.
Verify the binary data being parsed against the expected constant value defined in the `Const` construct. If the data is correct and the `Const` definition is incorrect, update the `Const` value. If the data is faulty, correct the data source.
Explicitly convert the `bytes` object to an integer using methods like `int.from_bytes(byte_object, byteorder)` with the correct byte order, or access individual bytes as integers (e.g., `byte_object[0]`). Conversely, convert integers to bytes using `int.to_bytes()` when building.
If the size depends on a context value, ensure that the necessary key is present in the context dictionary when calling `sizeof()` or when building. For dynamically sized constructs, `sizeof()` might not be determinable, and you may need to rely on parsing or building to calculate the actual size.
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