Introduction

This module contains a parser for dbus signatures constructed using the pyparsing library (http://pyparsing.wikispaces.com/).

The grammar follows the informal specifications at https://dbus.freedesktop.org/doc/dbus-specification.html. This grammar is a very simple one, parsable by an LL(1) parser.

The grammar has undergone significant testing using the Hypothesis testing library (http://hypothesis.works/).

Usage and Implementation Hints

Usage of the library to verify that a string is a signature is fairly straightforward:

>>> from dbus_signature_pyparsing import Parser
>>> parser = Parser()
>>> parser.PARSER.parseString("a(qy)", parseAll=True)

If parseString() does not raise a pyparsing exception, the argument string is a valid signature.

Note that the empty string is a valid signature. Thus, it is important to require that the parser parse the entire string by setting the parseAll parameter to True. If parseAll is False, which is the default, the parser can always parse the empty string, and every string will be parsed and verified to be a valid signature.

The Parser object exposes all its sub-parsers as instance attributes. The PARSER attribute is the top-level parser, suitable for parsing general signatures. The COMPLETE attribute parses what is defined in the informal specification as a “single complete type”. The CODE attribute is equivalent to the specification’s “type code”.

The parser is easily used either by delegation or by inheritance. Each sub-parser attribute is a ParserElement; consequently each sub-parser supports the addParseAction() method. To customize the basic parser to return a particular value as a result of having parsed a signature invoke the addParseAction() method on each appropriate sub-parser with an appropriately chosen method. The modified parser should then return the desired value when the parseString() method is invoked on a valid signature string. For further assistance, consult pyparsing’s extensive documentation at http://pyparsing.wikispaces.com/ and https://pythonhosted.org/pyparsing/.

Packaging

Downstream packagers, if incorporating testing into their packaging, are encouraged to use only the tests in the test_deterministic.py module, to avoid testing failures that may arise due to the non-deterministic behavior of Hypothesis tests.