construct-legacy 2.5.3

Example

A PascalString is a string prefixed by its length:

>>> from construct_legacy import *
>>>
>>> PascalString = Struct("PascalString",
...     UBInt8("length"),
...     Bytes("data", lambda ctx: ctx.length),
... )
>>>
>>> PascalString.parse("\x05helloXXX")
Container({'length': 5, 'data': 'hello'})
>>> PascalString.build(Container(length = 6, data = "foobar"))
'\x06foobar'

Instead of specifying the length manually, let’s use an adapter:

>>> PascalString2 = ExprAdapter(PascalString,
...     encoder = lambda obj, ctx: Container(length = len(obj), data = obj),
...     decoder = lambda obj, ctx: obj.data
... )
>>> PascalString2.parse("\x05hello")
'hello'
>>> PascalString2.build("i'm a long string")
"\x11i'm a long string"

See more examples of file formats and network protocols in the repository.

Resources

Construct’s homepage is http://construct.readthedocs.org, where you can find all kinds of docs and resources. The library itself is developed on github; please use github issues to report bugs, and github pull-requests to send in patches. For general discussion or questions, please use the new discussion group.

Requirements

Construct should run on any Python 2.5-3.5 or PyPy implementation.

Its only requirement is six, which is used to overcome the differences between Python 2 and 3.