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authorLivio Recchia <recchialivio@libero.it>2020-02-10 23:06:34 +0100
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+Construct2
+==========
+Construct is a powerful **declarative** parser (and builder) for binary data.
+
+Instead of writing *imperative code* to parse a piece of data, you declaratively
+define a *data structure* that describes your data. As this data structure is not
+code, you can use it in one direction to *parse* data into Pythonic objects,
+and in the other direction, convert ("build") objects into binary data.
+
+The library provides both simple, atomic constructs (such as integers of various sizes),
+as well as composite ones which allow you form hierarchical structures of increasing complexity.
+Construct features **bit and byte granularity**, easy debugging and testing, an
+**easy-to-extend subclass system**, and lots of primitive constructs to make your
+work easier:
+
+* Fields: raw bytes or numerical types
+* Structs and Sequences: combine simpler constructs into more complex ones
+* Adapters: change how data is represented
+* Arrays/Ranges: duplicate constructs
+* Meta-constructs: use the context (history) to compute the size of data
+* If/Switch: branch the computational path based on the context
+* On-demand (lazy) parsing: read only what you require
+* Pointers: jump from here to there in the data stream
+
+.. note::
+ `Construct3 <http://tomerfiliba.com/blog/Survey-of-Construct3/>`_ is a rewrite of Construct2;
+ the two are incompatible, thus ``construct3`` will be released as a *different package*.
+ Construct 2.5 is the last release of the 2.x codebase.
+
+ Construct 2.5 drops the experimental text parsing support that was added in Construct 2.0;
+ it was highly inefficient and I chose to concentrate on binary data.
+
+Example
+-------
+
+A ``PascalString`` is a string prefixed by its length::
+
+ >>> from construct 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 <https://github.com/construct/construct/tree/master/construct/formats>`_
+and `network protocols <https://github.com/construct/construct/tree/master/construct/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 <https://github.com/construct/construct>`_;
+please use `github issues <https://github.com/construct/construct/issues>`_ to report bugs, and
+github pull-requests to send in patches. For general discussion or questions, please use the
+`new discussion group <https://groups.google.com/d/forum/construct3>`_.
+
+Requirements
+------------
+Construct should run on any Python 2.5-3.3 implementation.
+
+Its only requirement is `six <http://pypi.python.org/pypi/six>`_, which is used to overcome the
+differences between Python 2 and 3.
+