JSON Regular Expressions

Motivation

Since PFA is JSON, it is easier to inspect, build, or edit if you have good tools for manipulating JSON. JSON is represented in Python as None, True, False, integers, floating-point numbers, strings, Python lists of the above, and Python dictionaries of the above. Titus's "JSON regular expressions" provide a declarative language for manipulating these structures.

"JSON regular expressions" work like regular expressions for text, except that they apply to tree structures, rather than substrings of text. The titus.producer.tools library provides classes for defining patterns, performing JSON-tree searches using those patterns, and using pattern-matches for extractions or modifications.

Keep in mind that, despite the name, these "regular expressions" are not matching the string representation of the JSON, but the Python structure (effectively a DOM).

JSON patterns

When you do from titus.producer.tools import *, you get a Python-based DSL for pattern matching. The pfainspector goes one step further and provides a shorter, regex-inspired syntax for the same pattern matching functions. The table below shows all of the patterns and their pfainspector equivalents.

Python class	Example	pfainspector syntax	Matches
NoneType	None	null	null and only null
bool	True, False	true, false	only true and false
int	123	123	exact number in JSON
float	3.14	3.14	exact number in JSON
str	"hello"	"hello"	exact string in JSON
list	[1, True, "hello"]	[1, true, "hello"]	exact array in JSON, may contain non-trivial patterns
dict	{"one": 1, "two": None}	{one: 1, "two": null}	exact object in JSON, may contain non-trivial patterns in the values (not keys)
Any	Any()	_	anything: any structure or leaf node
	Any(int, str)	(no equivalent)	specified Python classes